GCSE Maths Tuition Lesson 8 Probability Part 1

Maths Tutor Mitchell Dye
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Oct 31, 2025
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foreign
welcome back to another GCSE math lesson
I believe this is the eighth one today
we're going to be covering the first
part of probability so there are two
parts of this the second part is going
to be the extremely difficult kind of
exam questions that you can come up with
uh but this first part is going to be
mainly about conditional probability so
things like and it's not just going to
be the uh kind of probability tree
diagrams so make sure you stick around
for that
for the first one it says there are only
red marbles and green marbles in a bag
six red and four green mason takes at
random a model from the bag he doesn't
put it back into the bag and he takes
the second one complete the tree diagram
so what I would like uh
again in with probability kind of
questions it can help to draw a diagram
so we have one two three four five six
and we'll put little R's in here
so six red and then we have one two
three four uh green ones right
so the way these three diagrams work is
this is the when he put his hand in to
the bag and pulls out a marble right
there's a chance that it's red and
there's a chance there's going to be
green okay and then if it's red then the
next time he puts his hand in you have
those two possibilities of it being
again red and green
likewise if it's green then these two so
basically it shows you all of the
different outcomes from pulling out in
this case two marbles from a bag so good
evening Evie how are you
so essentially all we need to do here is
work out before he's pulled out the
first marble what is the what are the
odds of him getting a red versus a green
well in total when we work up
probability we look at the number of
ones that we want divided by the total
number of outcomes so that's a very
fancy way of saying okay so there are
six red marbles so I know the top of my
fraction is going to be six
now how many marbles do I have in total
well there are six red and four green
therefore in total there are ten
okay likewise for green well there are
four greens and until there are ten
now one thing to note about probability
tree diagrams is a good way to check if
you've done it correctly is that across
the branches it should add up to one
because all probabilities add up to one
so six over ten plus four over ten gives
me ten out of ten which is one so we're
correct there
and here's where it gets a bit tricky
okay let's look at the first possibility
where
when he pulls out the first marble it's
a red marble and he doesn't put it back
so if we wanted to draw that out we
could just put a line through here and
say well he's gotten rid of one red
marble
so now we need to point out the second
one what's the probability of him
getting red and a green
well how many red marbles do we have
left well there's one fewer so there's
five now so one two three four five so
the top is now going to be five
now how many there in total well we've
taken one marble out
right from this first section here so
there's only nine left
okay and again if we can't stop the
marbles here we have one two three four
five six seven eight nine
so the mistake that I tend to see
uh students make is that they don't take
away one from the top and the bottom
right so if a red Marble's taken then
the number of Reds decreases by one and
the total number also decreased by one
okay now likewise with the green well
there are still four greens left because
we didn't take a green out I have a
total of nine and again if you look
across the branches here
five at four is nine so we have nine out
of nine which is one
now what happens if you took a green
marble well the number of Reds doesn't
change so this is still a six
but the total number has decreased to
nine
and likewise with the greens now it
becomes three over nine
another question I get asked is if we
have to simplify the fractions so you
don't have to with probability tree
diagrams because it gets a bit tricky to
realize like they need to ideally be the
same so you don't need to simplify them
okay and it in some cases helps to not
simplify them
hopefully that will make sense again I
don't think probability tree diagrams
are too tricky there's just a few things
you have to remember
um and again the questions are going to
get more tricky as we go along
perfect so Part B says work out the
probability that Mason takes two marbles
of the same color and again this is
another place where students tend to
make mistakes okay the first thing you
need to do is write out the different
ways that he could take two marbles of
the same color so in this case he can
either take out a red followed by Red
or a green followed by a green
now it might seem fairly obvious in this
question but in some questions it can
get a bit tricky make sure you eliminate
every possible way of fulfilling this
condition
okay so red and a red
what we're going to do is read along
this probability tree so you fix a red
then another red
now when we go across the tree like
along it here we times the probabilities
so in this case we'll have 6 over 10
multiplying
by 5 over 9.
another way to look at it
is we want the probability of getting a
red
and another red now whenever I say the
word and in probability it means times
okay so the other way of writing this
would be probability of one red
and so I put a times a probability of
getting a second red
okay
6 times 5 gives me 30. 10 times 9 gives
me 90. now
I'm going to have to add probabilities
together so I'm not going to simplify it
just yet
what about green and the green well we
start off at this probability here
it's 4 out of 10.
and multiply it by this probability
which is for the second green
three out of 9.
now here's where some students get a bit
confused
they think that this is the answer but
it's not okay so
in order for me to get two marbles of
the same color
I can get a red and a red or
a green and a green
now whenever I say the word or I need to
add
okay so probability of the same color
is the probability of getting two Reds
30 over 90.
or so add
the probability of getting two greens
12 over 90. and again the reason for
that is because
sorry I've got a bit of a cold so it
might sound a bit uh under the weather
where was I okay so because we're saying
that there's two different ways of it
happening we need to add those
probabilities together
okay so in this case it's 42 over 90 you
can simplify if you want but you don't
have to
okay so you can say it's 21 over 45
leading divided by three as well
right there's m1421 that becomes seven
and that becomes 15 and that's as low as
you can get either way you don't have to
simplify with probability usually
unless they specify
and I don't think that was too tricky
but again the questions will gradually
very slowly get harder and harder okay
so even here this is slightly more
different more different more difficult
this is something called conditional
probability okay and I'll explain why in
a second
so each day Paul either wears a red or a
black tie to work on Monday the
probability wears a black tie 0.6
okay so I'm going to put that in right
now
probability on a Monday is 0.6
okay
now
if it says here he either wears a black
or a red tie those are the two options
so if the probability of in buying a
black tie 0.6
the informative him wearing a red tie
is 1 minus 0.6
and the reason for that is all
probabilities have to add up to one
okay
so
if Paul wears a black tie on Monday the
probability that he will wear black tie
on Tuesday 0.35 so black time Monday so
black time Tuesday is 0.35
and again we need to make sure it adds
up to one so that means the red tire is
0.65
. so the reason why it's called
conditional probability is this here is
a condition
if he wears a black tar Monday that's a
condition
then the probability changes okay so the
probability depends on what happens on
Monday so it's a condition okay but it's
really not that complicated it doesn't
really matter
if he does not wear a black tie on
Monday the probability that he will wear
black tan Tuesday 0.68 so again we can
fill that in
and again it needs to add up to one so
all we need to do is do one minus 0.68
which is 0.32
those are our two marks
are there any questions on that at all
is all about really reading quite
carefully
oh good perfect so again they're
gradually getting a bit more tricky but
not too bad so far I hope
and again
work out the probability pool wears
different colors Ties on Monday and
Tuesday so again this is where students
can get a bit
worked up in terms of
the probabilities so he has to wear a
different color tie so one red one black
so we can either wear the black tie on
Monday followed by the red tie on
Tuesday
or you can wear the red tie on Monday in
the black tan Tuesday
now there's no other combinations right
because either he wears two black ties
or two red ties which isn't a different
color tie
okay
so again we can work out these
probabilities now
Black Tie on Monday 0.6 so let's put 0.6
here
and then because we're moving across
sorry along the um
tree we times that by the red tie on
Tuesday 0.65
just so you're aware as well is the
first question we did can turn up on
non-calculator or calculator
because it's fractions but with decimals
it's only going to be
um
calculator paper okay unless they're
really easy decimals but these ones
aren't particularly easy I'll work those
out both together in a minute
red then black we have 0.4
multiplied by black which is 0.68 so
again if you notice I'm hesitating when
I'm saying it because again it needs to
be red then black some students multiply
the wrong probabilities they go red and
red or something all black and black for
example
so now we can pull up our
whoops not that
Katana put up our calculator
perfect so 0.6 multiplied by 0.65 gives
me 0.39
and then we also have 0.4 so
hey
which is 0.272
but again the probability of wearing a
different color
is
both of those things added together
okay
so answer plus 0.29
gives me
0.662 and that's our final answer and
again that's three marks
you might notice it doesn't really take
three marks worth of time but again it's
all about effort probabilities tends to
be one of the trickier topics because
people can lose marks Without Really
noticing okay so this is these kinds of
questions are the
most common for students to kind of lose
a Mark or two because they don't include
other probabilities or something else
okay so it's very easy to make a mistake
everything okay with that one
mm-hmm
I think that's all okay
can it gradually gets more difficult so
finding this easy that's good
perfect thank you Evie
so again
this one so you may have noticed in the
previous questions it kind of
holds your hand a little bit right
um it takes you through it but this one
is just a format question straight away
you have five red three blue counters
two cancers taken at random work out the
probability that one of each color is
taken
two ways to do this okay
the first way is to do what was given in
the previous question and draw a
probability tree
the other way is I like to like draw a
little diagram
five red counters
there are
three blues
so I can do the probabilities in my head
fairly easily but that's because of
practice
but again you can draw a probability
tree
now if we want to one of each color
either
a red is taken then a blue or a blue is
taken then a red right
now let's have a think about the
probability so I'm going to do this
without doing a probability tree because
we've already because I want to show you
a new way of doing it because in the
previous questions we've already done
probability trees Okay so
probably still taking a red right is
going to be the five Reds we have so
five
over the total number of counters one
two three four five six seven eight
and then again don't forget we need to
multiply because it's a red and a blue
now if we've already taken a red we can
put a line through red
now what's left over well we have our
three blues
over seven
okay
so again you don't need a probability
tree
but again this is just a different way
of doing it if you want to use a
probability tree that's a valid method
okay
so we've done that possibility and again
I'll work it out in a second
so probably getting a blue at the
beginning is the three blues we have
over the total number of um counters
which is eight
multiplied by the five Reds we have
over the seven that'll be left over if I
were to cross out blue
all okay with that
again just stop me if you uh need any
help with that
215.
then we can that
you might notice it's actually the exact
same probability
but once again
one of each color car so one of each
well
either one of those methods works right
so we're going to add we're going to
take the red blue
probability and add it to the blue red
because it's either or it doesn't matter
and that is a four mark question done in
three lines
so you can use a probability tree that's
valid
we can do it this way and is this method
okay is there any questions about that
at all
good we're going through these pretty
good yeah perfect thank you Evie perfect
so
Perfect all good
okay now here it gets a bit more tricky
right because we have three colors okay
so there's a few more combinations
but it's the same maths okay so again
let's draw a diagram out so we have one
two three four five these are Reds
we have one two three blues
and we have one two
great
again if you want we can do a
probability tree but it's going to be a
pretty big tree
but Billy takes two counters at random
from the bag work out the probability
that both of the counters are from the
same color
good so either it's two Reds or it's two
blues or it's two greens
fairly standard I think I think that's
okay
for Two Reds well how many Reds do we
have at first well we have five
and how many uh counters we have five
six seven eight nine ten
and again because it's and we need to
multiply and we get rid of one of the
Reds we have four Reds left over
and there's nine counters left over
again just feel free to stop me if any
of this doesn't make sense
two Blues well we have three blues at
the start out of ten
then one of them goes away so it becomes
two over nine
so again you can see that you can start
doing this a bit faster and faster and
faster okay but only once you're
comfortable
with the greens we start with two over
ten
and then one over nine
so again uh feel free to digest that and
stop me I'm just going to work out these
fractions
okay now once again we're looking for
the probability that both counters are
the same color not that they're red red
blue blue or green green
right so we need to add all of these
together
so
20 over 90
. so 20 add 6 is 26 plus 2 is 28 90. and
again you don't have to simplify if they
don't specify
okay so I think that's okay so far
hopefully
again that was a format question done
pretty quickly I think
okay
okay so in this one they actually give
us
the diagram
okay so I'm just going through a bunch
of different style of questions and they
should be in general getting harder as
we go along
so Helen takes a card at random she does
not replace it
Helen then takes another card at random
so so far all of our questions have been
this they don't replace okay now if they
don't say that they replace it then
assume that they don't replace it okay
if they replace it something different
happens so you need to be very careful
that it says this
or that it doesn't say they replace them
okay there's a question coming up I'm
pretty sure there has one where they
replace it the probabilities change
slightly like think about what would
happen okay
then takes another card at random both
cards have the same number well
either it's going to be a one one
or a two two or a three three
okay
what about probably getting a 1-1 well
at first they make two out of seven
right so there's two ones out of seven
cards then one of the seven goes away so
we have one one left over one one
out of six total cards
tutu once again it's two over seven
and it'd be one over six again because
there's only two cards cross one out
look at that
three threes we have three over seven at
the beginning
multiplied by two over six
it's gonna make sure you can see when
I'm getting all these fractions from uh
just while I work this out so we have
two over forty two
we have 2 over 42 again then we have six
over forty two
and once again it's asking for
probability both cards have the same
number so
two plus two plus six would be 8 over
42.
so again we're doing these questions
pretty quickly
now the second part
this is the style of question that can
get a bit more interesting okay
definitely a higher paper question
definitely towards the end
to calculate the probability that the
number in the second card Helen takes is
greater than the number on the first
card she takes there's a
uh is that the answer to Part B
or oh
well spotted TV
two plus two plus six is ten not eight
I'm sorry
I'm dosed up on a lot of medicine at the
moment yeah that is completely correct
that is a 10 well spotted
cool
uh this isn't an actual exam paper Lila
so I've actually gathered a bunch of
questions from different exam papers and
also from math Genie okay
so this isn't actually a specific paper
um in terms of what paper can it come up
in so it can come up in paper one two or
three
but mainly It's Paper one or two
okay if it has decimals it's only paper
two because it's calculator if it's
fractions it can come up in paper one or
two
okay
so calculate property okay see it we
have a bunch of different combinations
okay
so either
if she picks a one first
then the second card must be greater
than one so it can either be a two
or it can be a three
okay
if you picks a two then the second
number has to be a three
and she can't have picked a three
right because you've picked a three
there's no number bigger than three
is that okay for the three combinations
we have are there any questions about
that
foreign
card yeah perfect
sweet a lot of I think I know you mean
there's no question so good so probably
to getting a one and then a two uh so
obviously getting a one was two over
seven if we remember rightly
ah perfect thank you Lila and then
getting a two afterwards well if we get
rid of a one
we still have two twos left out of six
that would be two over six
likewise if we have a seven we have uh
sorry a one and three so that'd be two
over seven times and we actually have
three threes left
so that'd be three over six
I may not have left myself from most
amount of space but yeah
then we pick a two first so that's two
out of the total seven
multiplied by will we get rid of one of
the twos and it has to be a three so
three out of six
so that would become four
over forty two I'll try and make sure I
can add basic numbers now so 6 over 42.
and this will always be six over two
and then probability
um
I'm not going to write the whole thing
out
it's going to be 4 over 42 plus 6 over
42 that's ten so be 16 over 42.
this time I didn't make a mistake
should be it
it's getting slightly trickier in terms
of what they can ask you this can be
anything okay so you have to be
um if there's one thing to take away
from the lesson make sure you understand
my logic
because this kind of question won't turn
up
but they'll change what the condition is
and unfortunately there's basically an
infinite number of conditions they can
give you
mm-hmm
okay
uh this one's interesting so 50 people
asked if they like tea coffee and hot
chocolate
and everyone I liked at least one of the
drinks
17 likes or three blah blah
this type of question
right when they give you information
like this
okay
it's always so if I if I draw blocks
here you have to draw
a then
diagram you have to
this information is way too complicated
to try and piece together yourself
okay
hopefully you can see why
Nutri exclusive okay so the word mute
sorry the term mutually exclusive
actually I don't know why I'm writing
mutually exclusive just means that both
events cannot take place at the same
time
okay
so the word exclusive means that it's
kind of apart from everything right like
an exclusive Club means that certain
people can't come in mutually means that
it can't happen for both of them
okay so mutually exclusive means that
both events cannot take place at the
same time
so for example if the probability it's
raining tomorrow is 0.4 probably if it's
sunny tomorrow 0.6
those two events are mutually exclusive
because they can't happen at the same
time for example
hopefully that clears up your question
so we have to draw a Venn diagram uh is
everyone okay and this is a five month
question
is everyone okay with what a Venn
diagram is
I hope so okay
okay so what you need first is we need a
circle for each of these three things
and they need to overlap so this is
where things get a bit messy so
we say that's for t
then coffee has to
overlap
and then hot chocolate needs to overlap
as well
page so T is for T C is for coffee and H
is for hot chocolate in fact let's do HC
for hot chocolate maybe that'll make it
a bit more
meaningful
cool now we have to read this uh one by
one
so with Venn diagrams you always start
from the middle and work out Venn
diagrams tend to be something quite easy
for students but they always make
mistakes in the exam so again those of
you that are tuning in
I'm willing to bet you're pretty clever
right and you can understand maths with
a bit of help okay it's fine
the problem is is human beings tend to
get a bit arrogant right and when we
find something easy we rush it and we
make mistakes when you come to sit your
exam or your mocks or whatever
you'll find that you'll answer every
question but won't get a hundred percent
because you've made mistakes okay
so with this be it's so easy to make a
mistake with this it's unbelievably easy
okay really really easy so you start
from the middle of the Venn diagram and
work outwards okay so you've worked from
the three-way intersection then the
two-way ones then then the outer ones
okay now the good thing is is that this
information is written in order that you
should add it okay actually no it's not
never mind uh you'd have to work out
your way out from from this stuff okay
well I'm glad that I've managed to give
it to you if you work from the outwards
in you won't get it correctly so for
example 31 people like hot chocolate
right
that's what it tells me
so
all of the numbers in the hot chocolate
Circle should add up to 31.
so we're going to have a number here
here here and here all four of those
numbers should add up to 31. so starting
from the out is basically impossible
right I can't write 31 here
because that's not true the total is 31.
yeah good so you need to look at the the
unions the interceptions okay
so just be very aware of that try and
work your way from the innermost to the
outermost so the innermost is all three
people sorry one person likes all three
drinks 17 people like all three drinks
there we go
now let's try and work out how many
people like tea and coffee
so
okay actually coffee and hot chocolate
but not tea
so they like coffee and hot chocolate so
that would be this intersection over
here is two
okay
then seven people like tea and hot hot
chocolate but not coffee so they like
tea and Hot and Hot Chocolate so that'd
be seven over here
so if I was like okay
so this question is a bit tricky because
they haven't actually given us
some of the um information
so sometimes they're quite nice and
they'd give us tea and coffee as well
but they haven't been very nice
okay so we don't know this number
and we can't work it out
just yet
right actually we can
tea and coffee
can work it out okay so again sometimes
they give you directly what tea and
coffee is uh like together but we can
actually work it out pretty uh easily so
third coffee
so
it says here so I also like to tick off
the information as I use it right so
I've used this I've used this I've used
this
so now all I'm looking at is these three
pieces of information
so again I like to start from the end
and work my way out so let's look for
the one that says and which is this
piece of information here 21 people like
tea and coffee
right so what some students do is write
21
here
it's not correct
okay
for tea and coffee we're looking at the
intersection between these two circles
which is both of these numbers here
so 17 plus the number in this bit
add up to 21.
so in this case it's going to be
4.
that's probably the first thing I've
said that might be pretty tricky
any questions about that
so do you mind me you're okay perfect
Lila and Evie are you good with that
it's a bit tricky
so tea and coffee is this intersection
here
that adds up to 21 okay perfect
wonderful so now we've done all of the
inner bits we have to now work out the
outer bits uh there is one thing we can
say every person likes at least one
drink which means the number outside the
circles is zero
because everyone has one everyone's in
at least one Circle
good I'm glad that that was okay so far
the next thing we realize is let's look
at the number of people that like tea
so 34 in total right
so everyone in this circle here should
add up to
31. okay so the number in here is going
to be
31 minus 4 minus 17 minus 7.
okay
so 7 17 that's uh 24 28 so it's going to
be 3.
hang on if I
7 and 17 is 24.
28 yeah
also it's 34 people my bad my bad
so add-on three that should be a six
my math was right I just chose the wrong
number
so the number in there is going to be
equal to
six showing you the um the way I'm
working I was helping
but again stop me the second you don't
understand
so we've used that piece of information
now
one more piece of information 31 people
liked hot chocolate let's do the same
thing
31 minus seven minus 17 minus two so 7
and 17 is 24 26 so that should be equal
to
5.
and there'll be an X in the middle of
17.
uh in the middle of 17.
as in the middle of this one or when I
was calculating it
so as in in this middle 17 here should
there be an X or when I was calculating
it just now
hmm
okay
so while you tap that I'm just going to
continue so in the last bit we need to
work out how many people are in here
ah good question Ed yeah so this counts
as working out
okay so if you look this is a five mark
question
if you manage to do the probability by
hand as in writing out whatever that is
you'd get four marks but this is all
method marks
so you get three marks for this Venn
diagram
a mark 4 of the probability calculation
and another Mark for the right answer
okay good question really good question
you get marks for the Venn diagram okay
because this does take a long time
you get up to three marks for it so with
the coffee
so we use that information
where Everyone likes one drink
so
if we do 50
take away all of the rest of these
numbers so for
we will get our final answer
you can still get method marks
so
for example if I've read this as like 40
instead of 50.
there's something called error carried
forward
something called ECF which you'll see in
your mark schemes where if you make a
mistake
they can reward method marks for the
following parts
okay so you don't just lose all the
marks if I read this as 40 though
they wouldn't give any marks
they might give some error carried
forward marks but you'd lose a lot
so
um
yeah
so you know what I'm going to be lazy to
do this on a calculator uh
so 50 minus 4 minus 17 minus 7 minus 2
minus 6 minus 5.
9 perfect that makes my life easier
cool so we've gained most of the marks
already
so we need to do now is work out the
probability that they both like coffee
if 50 people are chosen at random so the
people number of people that like coffee
are all of these people in the diagram
here
so we have nine
plus four plus Seventeen plus two
thirteen Thirty thirty two people
probably said they both like coffee
it's going to be 32 over 50.
now they won't choose the same person
again so we subtract one from the number
of people that like coffee and one from
the total number of people
okay and once again
should be a calculated paper question
but if it's not
it doesn't matter
992 you can do this by hand I know
but I don't think you want to watch me
just do
like you know column method
multiplication so
2450.
and that is five marks
long question not gonna lie
but it is five marks so it's expected
you can do this Venn diagram a lot
faster than what I did bear in mind I
spoke through everything I did so I'm
willing to bet you guys can eventually
write this pretty quickly
any questions at all about that
that's okay
good
yeah
uh another question which is
pretty
pretty annoying
it's another Venn diagram question but
you know it's good to kind of practice
apples bananas and oranges so let's just
real quick blast this one at least would
start a bit faster than this um
sorry for stumbling over my words like I
said I'm a bit sick so
apples it's a nice
I'm trying to make sure that my overlap
is big enough that you guys can actually
read
what's happening
this box
okay
so once again we start from the middle
so
it's roughly an order of when we're
going to use it 11 people like all three
so that makes our life
slightly easier
and again take off the piece of
information
30 people like apples again I like to
work my way out so I'm gonna skip that
six people like apples and bananas but
not oranges
so apples and bananas is here
not oranges so that should be six there
right because again we're not including
the people that like oranges so they
shouldn't overlap
Okay so
15 people like bananas and oranges so
again that's in total so this should be
four
because again it doesn't specify
that they don't like apples
five people don't like any fruit so
those people are gonna go straight
outside the Venn diagram
and all 25 people who like oranges
like at least one other fruit
so that means all three numbers here
should add up to 25.
11 plus 4 is 15 10 uh
so where does the four come from Lila
okay so it tells me here
15 people like bananas and oranges
okay
now all the people that like bananas and
oranges are in this intersection here
those two parts
so those two numbers should add up to
15.
does that make sense Lila
okay perfect uh does the 10 make sense
I did hurry through that explanation
just to get to Lila's question so
cool sorry for that noise by the way
I've muted it
okay now we can start working our way
out right so 33 people like apples
is where that six is
not quite it would be a
and then the N symbol B
and not C
because you're saying it's or Nazi right
so it'd be something similar to this so
foreign
come from okay so
if you look here Jemima it says that 15
people like bananas and oranges
so
if we look at where bananas and oranges
we're looking for this
the overlap between bananas and oranges
which can you see as this overlap here
so the bit right in the middle and the
bit over here
those two numbers should add up to 15.
so I knew that 11 plus something had to
add to 15 that something had to be 4.
does that make sense
so I hope that makes sense okay
so 33 people like apples so everything
in this circle here should add up to 33.
currently I have 10 plus 11 which is 21
plus 6 which is at 27.
so to get to 33 I'll need another
six
I hope that makes sense
okay now if you won you can actually
write a zero in where this part is
because again everyone that liked
oranges liked other fruit as well
okay so we there's zero in just the
oranges so now
everyone else needs to be in just the
banana column
column uh Circle
so
we're doing 50 minus 5 minus six minus
six minus 11 minus ten and minus four
and that will give us everyone that's
left over which is in the banana
um Circle
so
50 minus five minus six minus six minus
11 minus 10 minus
again you can do this in your head I'm
being a bit lazy
and that's our Venn diagram we did it a
lot quicker but we can do it even faster
this is here to the 50 people are chosen
at random work at the probability they
both like bananas
so
how many people in total like bananas
well we have
eight plus six plus eleven plus four
okay so six plus four
10 21 29 people
so you have 29 out of the total 50
multiplied by we subtract one because
they're not going to pick the same
person twice
over 49.
and let's just use a calculator again
you can do this by hand
and if you want me to show you how to do
it I'm more than happy to
um but I I think everyone here is okay
with column multiplication
58 over 175.
I think that's too bad
any questions about that at all
I think that's okay
okay
all right perfect so we only have 10
minutes left and I actually split
probability in two okay probability can
be one of those unseen super hard
questions the ones where they have like
algebra in it and ratios and all this
other stuff
we're going to do that next week there's
no point of me doing it now because we
only have 10 minutes and it gets a bit
more intense but the stuff we've mainly
covered today is probability trees
and the Venn diagram kind of questions
so those should hopefully be okay
but next week is
the hardest probability questions you'll
find
okay so I'm not looking forward to it
but again if you get good at it it's
going to be um yeah it is exciting but
probability is really easy to lose marks
on because again you can miss out on one
combination and you get the wrong answer
you'll get method marks don't worry
about that but it is where pretty much
all students will lose at least one mark
okay
so if you get like 98 in your test
you'll know why it's probably a
probability question
but again only 10 minutes I don't I
don't think it's fair for me to just
shove this
in now you guys have worked really hard
so we can finish slightly early but next
week will definitely go through the
harder probability
[Music]
um
thank you Lila I really appreciate it um
honestly at the moment it's just a bit
of a
it just hurts to talk
so everything else is pretty much fine
um
oh it's worth studying yeah but honestly
so this is going to sound a bit cringy
but probability is more of a mindset
okay it's less equations and more
thinking logically about what they're
asking you to do what are the
combinations what are the situations
you're in Okay so
yeah it's a bit more
a bit more of a mindset than it is uh
calculations
okay
yeah it's one of the tricky ones after
probability I want to ask you guys what
would you like to do next so vectors is
probably
the hard actually
factors is one of the tricky ones as
well so we can do vectors for sure
I know it's in all three papers Evie
and it's definitely likely to come up in
at least two
so that like the length of a line
um
we can do that
we can do that
yeah it's I think they just call it
coordinate geometry
that's just what they call it but that
has like everything in it just
everything like mid points um equations
of lines perpendicular bisectors all
that also includes like lengths of lines
as well
yeah do ratios yeah
so ratios length of line yeah cool so
I'll write those down
but we will cover everything but some
topics are pretty some people just don't
care about them so no one really Tunes
in so I don't bother doing them just yet
I will say that soon I'm going to be
doing topic summaries of the whole there
are seven topics in GCSE maths I'm gonna
do big topic summaries of all of them so
you have like algebra numeracy ratios
Etc
yeah
okay
again I think vectors is pretty tricky
but we can save that for a bit later
this covers the next three lessons now
so it's fine
okay if that's everything I hope you
guys enjoy your evening you're probably
on half term at least I am as well uh so
enjoy your half turn take a bit of a
bit of a break okay don't work too hard
and yeah
very welcome but yeah definitely don't
work too hard burnout is very real okay
you can drive yourself a bit crazy
I appreciate that thank you both for
your kind words and thank you for tuning
in as well it's always good to see you
guys
yeah
then definitely take a break
okay definitely
if you get burned out you're going to do
really badly in the exams even if you
know what to do
some time off
okay
I know you've probably got to set a ton
of homework but
yeah
take a bit of a relaxing a relaxing
break
although the weather's terrible
very welcome
yeah perfect I will see you guys
yeah so I'll see you guys next week
um again enjoy your half time you've
definitely earned it
and yeah we'll cover the harder parts of
probability and then we've probably gone
to length of lines or ratios and things
like that
yeah
see you guys later
