If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:2:40
CCSS.Math:

Video transcript

let's see if we can add nine point zero eight seven to fifteen point three one and I encourage you to pause the video and try to do it on your own so I'm assuming you have tried to do it on your own and now let's see how we could actually tackle this now one thing I want to point out some of you all might see these numbers all lined up and immediately want to say hey 7 plus 1 is 8 and 8 plus 3 is 11 carry the 1 etc etc and if you did that you would be making a mistake because you see right over here these decimals aren't lined up here you if you did that you would be adding the 7 thousand to 100's you would be adding 0 tenths to 5 ones you would be adding 9 to 1 tens or essentially this is a 10 right over here so the places would be all mixed up so what you need to do is actually align the decimals so that your place values are aligned so what you want to do is you want to align things up so we could write nine point zero eight seven and then we want to align the decimal so let's align the decimal this is what has to match up and this is going to be 15 point three one and this should hopefully make sense to you as well this is 9 point something plus 15 point something so it's going to be if you add a nine to 15 you get it'll be 24 point something give or take a little bit so when you see that here that here you have a nine plus the 15 so you've lined up the appropriate place values and now we are ready we are ready to add it's a good idea to start with the smallest place value so if you have any extra at a certain place you can bring in to some you could bring something into the next place value so here you say seven plus well I know this is 7 thousandths it's in the thousands place and you might want to say well what do I add it to there's no thousandths right over here and you're right there are no thousand so we could literally write 0 thousandths so 7 thousandths plus 0 thousandths is seven thousand eight hundred plus one hundredths is nine hundredths 0 plus 0 tenths plus three tenths is three tenths we got our decimal then you have nine one plus 5 ones is 14 ones well 14 ones is the same thing as four ones and one 10 so we'll carry that one right over there this is just one 10 plus four ones is 14 and so then finally you have one 10 plus another 10 is 2 so we get 24 point three nine seven