7th grade foundations (Eureka Math/EngageNY)
Sal solves 9.087+15.31 using the "standard algorithm". Created by Sal Khan.
Let's see if we can add 9.087 to 15.31. 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 have seen 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, et cetera, et cetera. And if you did that, you would be making a mistake. Because, you see, right over here, these decimals aren't lined up. Here, if you did that, you would be adding the 7 thousandths to 1 hundredths. 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 to 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 9.087. 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 15.31. 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 9 to 15, it will be 24 point something, give or take a little bit. And you see that here. Here you have a 9 plus the 15. So you have lined up the appropriate place values. And now 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 something into the next place value. So here you say 7 plus-- well, this is 7 thousandths. It's in the thousandths place. And you might want to-- you say, well, what do I add it to? There are no thousandths right over here. And you're right. There are no thousandths. So we could literally write 0 thousandths. So 7 thousandths plus 0 thousandths is 7 thousandths. 8 hundredths plus 1 hundredth is 9 hundredths. 0 plus 0 tenths plus 3 tenths is 3 tenths. We got our decimal. Then you have 9 ones plus 5 ones is 14 ones. Well, 14 ones is the same thing as 4 ones and 1 ten. So we'll carry that 1 right over there. This is just 1 ten plus 4 ones, which is 14. And so then finally, you have 1 ten plus another ten is 2. So we get 24.397.