Subtracting Fractions with Unlike Denominators (Part 2) | Math with Mr. J

[Music] welcome to math with mr j [Music] in this video i'm going to cover how to subtract fractions with unlike denominators and this is part two so if you're looking for part one i drop that link down in the description if you're ready for part two let's jump into number one where we have seven eighths minus three fourths and the first thing that we need to do is find a common denominator now you may recognize what that common denominator is right when you look at the problem if not we need to write out some multiples of both 8 and 4 and look for that least common multiple that's going to be our common denominator i'm going to come to the bottom of the screen where i have some extra room to write out the multiples and we'll look for that least common multiple that will be our common denominator we'll start with eight so my suggestion would be write out four or five for each look to see if you have any common multiples specifically the least common multiple if not you can continue your lists until you find the least common multiple so 8 16 24 32 let's do four so 4 4 8 and we don't need to continue because we see that we have a common multiple and specifically a least common multiple of eight between eight and four so we are ready for our next step so eight is going to be our common denominator i'm going to come back up to the original problem just underneath and start to rename these fractions with that denominator of 8. so once i have that common denominator i need to rename my fractions with that denominator of 8 i'm going to use equivalent fractions in order to do so now 7 8 already has a denominator of 8 so i don't need to rename i can bring that seven straight down as far as three-fourths i need to think how do i get that denominator of four to equal the denominator of eight four times what equals eight well i know that four times 2 equals 8 so whatever i do to the denominator i have to do to the numerator in order to keep these fractions equivalent i don't want to change the value of the problem at all so i need to multiply the numerator by two as well three times two gives us six so six eighths is equivalent to three fourths we now have that common denominator of 8 so we are ready to subtract when we subtract fractions we subtract the numerators so 7 minus 6 gives us a numerator of 1 in our answer and we keep our denominator the same we keep it 8. so our final answer is 1 8. now we always look to see if we can simplify our answers but 1 8 is in simplest form the only common factor between one and eight is one so it is again in simplest form and we are done so the answer to number one is one eighth let's move on to number two and try another one so we have 4 6 minus 8 15. we need a common denominator so let's write out some multiples of 6 and 15 and see if we can find that least common multiple which will be our common denominator we'll start with 6 and we'll write out 4 multiples so 6 6 12 18 24. all right let's do 15 now so 15 15 30 45 60. and we do not have any common multiples so what we can do we can extend our lists now the multiples for 15 we're already at 60. the multiples for six we're only at 24. so let's extend that list so the next multiple is going to be 30 and that's going to give us a common multiple specifically the least common multiple so 30 is going to be our common denominator let's go back up to the original problem and rename these fractions with that denominator of 30. so let's do 4 6 first so how do we get 6 to equal 30 well we know 6 times 5 gives us that denominator of 30 so we need to do the same thing to the numerator in order to have an equivalent fraction so multiply 4 by 5 as well so 4 times 5 is 20. so 20 30 is equivalent to 4 6 and we now have that denominator of 30. now we need to do 8 15. so 15 times 2 is thirty do the same thing to the numerator eight times two is sixteen so we have twenty thirtieths minus sixteen thirtieths twenty minus sixteen subtract the numerators that gives us 4 keep the denominator of 30 the same so 4 30 is our answer but we can simplify 4 and 30 have a common factor of 2 so let's divide both by 2 and this will give us the simplest form so 4 divided by 2 is 2 30 divided by 2 is 15. so our final simplified answer is 2 15. now if you need more help or clarification with simplifying fractions i dropped a link to my video about simplifying fractions down in the description as far as subtracting fractions with unlike denominators remember find a common denominator rename with that common denominator subtract and then look to see if you can simplify that answer i hope that helped thanks so much for watching until next time peace