welcome to math with mr. J in this video I'm going to be doing a decimal review so a refresher on how to add subtract multiply and divide decimals so hopefully if you need a little more help with one of these operations this helps you out now if you're looking for a little more in-depth instruction or more examples I dropped the links to my videos on adding subtracting multiplying and dividing decimals below in the description so let's jump right into number 1 here where we have addition so 18 and 4/10 plus 3 and 97 hundredths so for adding and subtracting decimals the most important part is lining the problem up correctly and you do that by lining up your decimals so 18 and 4/10 plus 3 and 97 hundredths now the problem looks a little offset that's fine we can use placeholder zeros because zeros to the right of a decimal do not change the value so I can put a 0 here to the right of that 4 and it doesn't change the value it's an equivalent decimal so now it looks a little neater and more lined up so once you have your decimals lined up and any placeholder zeros put into place we can just add so 0 plus 7 is 7 4 plus 9 is 13 bring my 1 over here now decimals line up throughout the whole problem so bring it straight down 1 plus 8 is 9 plus 3 12 1 plus 1 is 2 so our answer is 22 and 37 hundreths now let's take a look at our original problem with decimals it's good to always see if your answer makes sense and we can use estimation so this number 18 and 4/10 is around 18 and the second number 3 and 97 hundredths if we were to round that to the nearest whole it would be around 4 so 22 is a good estimate so our answer 22 and 37 hundredths is a reasonable answer if you put the decimal in the wrong place or forgot the decimal it should tell you that something went wrong because that answer doesn't make sense so let's take a look at number 2 again adding and subtracting the most important thing line your decimals up so here we have 34 and 6 tenths minus 4 and 864 thousandths now that problem looks even more offset than the first one that's okay because we lined our decimals up the most important part and when you line your decimals up it lines all of your places up so now we need a couple of placeholder zeros now we're all lined up and we have our placeholder zeros I cannot do 0 minus 4 I need to borrow so I can't borrow from this zero so I need to borrow from the 6 it's now 5 this zero turns to a 10 but I need to bring the 1 over all the way to the right so it's going to be a 9 and then the zero to the far right is now a 10 so 10 minus 4 is 6 9 minus 6 is 3 I cannot do 5 minus 8 so I need to borrow from the 4 which now becomes a 3 so I get 15 minus 8 which is 7 bring my decimal straight down I need to borrow again from the 3 which is now 2 and that other three now becomes a 1313 minus four is nine and then bring my two down 2-0 there would give me two so 29 and 736 thousands so let's estimate here let's do an estimation so 34 and 6/10 would round a 35 four and eight hundred sixty-four thousands would round the five so 35 minus five our estimation would be thirty so our actual answer is reasonable it makes sense let's check number three as we move to multiplication so for multiplication you don't necessarily have to line that decimal up I find it easier let's take out the decimals to start with and we are going to do 52 times 45 again I took out the decimals I'm going to put them in at the end five times two is ten five times five is 25 plus 126 done here done here we need our zero here as we move to the next place 4 times 2 is 8 4 times 5 is 20 now we add our partial products 0 plus 0 0 6 plus 8 is 14 1 plus 2 is 3 and we have our 2 here now we need to put our decimal back in to our answer so we take a look back at our original problem and we need to see how many digits are to the right or behind a decimal well we have this 2 here so that's 1 and we have this 5 here so that is 2 two digits behind the decimal so our answer needs two digits behind the decimal so we bring it in one two and it goes right here or think of it as one two digits behind the decimal in our answer so for number three the product is 23 and 40 hundredths and if we take a look at our original problem we have something around five times something around five so our answer should be somewhere around 25 so our answer is reasonable we know we put the decimal in the correct place so for number four we have dividing decimals so let's set it up three and two tenths is our divisor and thirteen and seventy six hundredths is our dividend so when you get to division problems the first thing we need to check is is the divisor or outside number hole if not we need to make it a whole number here we have three and two tenths so it's not exactly a hole so we need to move this decimal to the right one time to make it a whole number this is going to make our problem much easier now whatever you do to the outside you have to do to the inside everything needs to stay balanced so we moved it once to the right on the outside so we need to move it once to the right on the inside now we can rewrite our problem so we have 32 as our divisor and we have 137 and six tenths now that the divisor is whole we bring this decimal straight up that's where it's going to be placed in the answer so if you have a whole number on the outside right off the bat you can bring that decimal straight up right away but here in this case we did not so now we can go through our long division steps can we do one divided by 32 no can we do 13 divided by two I'm sorry 13 divided by 32 No so we need to do 137 divided by 32 and 32 can be pulled out of 137 four times that gets us to 128 so we'll subtract we get nine bring down this six so now we have 96 divided by 32 which happens to give us three we can pull three whole thirty twos out of 96 and 96 and 32 are compatible so we hit it without any remainder so three thirty twos out of 96 three times 32 like we said hits 96 exactly our answer is 4 and three tenths so if we take a look at our original problem we have something around 14 here divided by 3 so 14 and 3 aren't necessarily perfectly compatible but we can think how many whole threes can we pull out of 14 well four whole threes that gets us to 12 and then we'll have a little leftover so this answer makes sense right because we pulled four whole three and two tenths out of 13 and 76 hundredths with a little left over so this answer is reasonable say for example you forgot to put the decimal and you got an answer of 43 you can look back at the original problem and think well that answer doesn't really make sense it's not reasonable maybe I did something incorrectly and you can figure out where you need to put the decimal so there's the quick refresher slash decimal review hopefully that helped thanks so much for watching until next time peace you