Adding and Subtracting Decimals: A Step-By-Step Review | How to Add and Subtract Decimals

[Music] welcome to math with mr j [Music] in this video i'm going to go through a quick review of adding and subtracting decimals this should be helpful for anyone looking for a quick refresher whether you're in middle school high school college continuing your education as an adult really no matter what class or goal you are working towards here are some examples to help you out now we're going to start with adding decimals let's jump into number one where we have nine and six tenths plus three and eighty-seven hundredths now when we add decimals the first thing that we want to do we want to line the problem up correctly and we do that by lining the decimals up that's going to line up all of our places so let's rewrite this problem vertically so up and down underneath here nine and six tenths plus three and eighty-seven hundredths so our decimals are lined up that means our places are going to be lined up now the problem does look a little offset because nine and six tenths goes to the tenths place and then three and eighty-seven hundredths goes to the hundredths place so what we can do here to make this look more lined up we can use placeholder zeros remember zeros to the right of a decimal do not change the value of that decimal so we're going to be working with an equivalent decimal we're not changing the value of the problem at all so we're able to use placeholder zeros to the right of a decimal so let's put a zero here in the hundredths place and now both of our numbers go to the hundredths and we're able to add so we'll start with the hundredths zero plus seven is seven then we'll move to the tenths six plus eight is fourteen so we carry our one now our decimal goes straight down into our answer it's lined up throughout the entire problem now we'll move to the ones place where we have one plus nine plus three one plus nine is ten plus three is thirteen so we'll put our three and then our carried one will be brought straight down and we end up with thirteen and forty seven hundredths let's move on to number two where we have 124 and 792 thousandths plus 84 and 5 tenths so let's line our decimals up here 124 and 792 thousandths plus 84 and 5 tenths so let's use placeholder zeros to line this up a little better here a zero in the hundredths and then a zero in the thousandths again zeros to the right of a decimal do not change the value of that decimal it's an equivalent decimal so we're able to use those placeholder zeros now we can add so we'll start with the thousandths place two plus zero is two the hundredths place nine plus zero is nine the tenths place seven plus five is twelve so we'll put our two and then carry the one we can bring our decimal straight down into the answer now we have the ones place one plus four is five plus four is nine the tens place two plus eight is ten so we'll put our zero here carry the one and then the hundreds place one plus one is two so we end up with 209 and 292 thousandths that's how we add decimals let's move on to subtraction so here are our examples of subtracting decimals let's jump into number one where we have 14 and nine tenths minus eight and fifty-seven hundredths now just like when we add decimals when we subtract decimals we need to line the decimals up that's going to line up all of our places so let's rewrite this first problem vertically here lining up the decimals so fourteen and nine tenths minus eight and fifty-seven hundredths so the decimals are lined up and that's going to line up all of our places now that problem looks a little offset because fourteen and nine-tenths goes to the tenths place and then eight and fifty-seven hundredths goes to the hundredths place so just like when we add decimals we can use placeholder zeros to have this look more lined up so let's use a placeholder zero in the hundredths place here and then both of our decimals go to the hundredths place remember zeros to the right of a decimal do not change the value that's an equivalent decimal and does not change the value of the problem at all now we're able to subtract so we'll start with the hundredths place we have zero minus seven which we need to borrow so let's borrow from the nine that's an eight now and we have ten minus seven which is three then we move to the tenths place eight minus five three bring our decimal straight down into the answer the decimal is lined up throughout the entire problem then we move to the ones place four minus eight we need to borrow from the tens place here so that's a zero and that's a fourteen so fourteen minus eight is six and we are done six and thirty three hundredths now i do wanna mention one more thing before moving on to number two and this is going to be a common mistake that you'll want to avoid and using placeholder zeros will actually help you avoid this mistake so let me rewrite the problem here real quick to the side so we have 14 and nine tenths minus eight and fifty seven hundredths so dropping this seven so starting with the hundredths place and then just dropping the seven because there isn't anything above it is not correct we actually have zero minus seven there so we needed to borrow and you can see we do not have a 7 in the hundredths place in our final answer so again avoid the mistake of just dropping that number because really we have zero minus seven there and we need to borrow so be careful of that let's move on to number two where we have 262 and 33 hundredths minus 59 and eight tenths so we will start by lining up our decimals here so 262 and 33 hundredths minus 59 and eight tenths we can use a placeholder zero so these both go to the hundredths and now we are able to subtract so we'll start with the hundredths three minus zero is three the tenths place three minus eight well we need to borrow so borrow from the two that's a one and we have a thirteen so thirteen minus eight is five we can bring our decimal straight down into our answer and now we have the ones place so 1 minus 9 we need to borrow so we'll borrow from the 6 and we have 11 minus 9 which is 2. then for the tens place we have five minus five which is zero and then lastly we have the hundreds place where we have two minus nothing under it so it's just two minus zero which is two and our final answer 202 and 53 hundredths so there you have it there's how you add and subtract decimals i hope that helped thanks so much for watching until next time peace