Current time:0:00Total duration:2:24
0 energy points
Sal has to borrow from a 0 to subtract 301-164. Created by Sal Khan.
Video transcript
Let's try to subtract 164 from 301. I encourage you to pause the video and try it on your own first. So let's go place by place. And we can realize where we have to do some borrowing or regrouping. So the ones place, we have an issue. 4 is larger than 1. How do we subtract a larger number from a smaller number? We also have an issue in the tens place. 6 is larger than 0. How do we subtract 6 from 0? So the answer that might be jumping into your head is all we've got to do is some borrowing or some regrouping. But then you might be facing another problem. You'd say: "Okay. Well, let's try to borrow from the tens place here." So we have a 1, if we could borrow 10 from the tens place, it could be eleven. But there's nothing here in the tens place! There's nothing to borrow so what do we do? So the way I would tackle it is first borrow for the tens place. So we have nothing here so let's regroup a hundred from the hundreds place. (So that's equivalent to borrowing a 1 from the hundreds place so that's now a 2.) And now the tens place instead of a zero, we're going to have a 10. Now let's make sure that this still make sense. This is 2 hundred plus 10 tens. 10 tens is a hundred. Plus one. 2 hundred plus a hundred plus 1 is still 301. So this still makes sense. And the reason why this is valuable is now we have something to regroup from the tens place. If we take 1 of these tens (so now we're left with 9 tens) and we give it to the ones place. So you give 10 plus 1, you're going to be left with 11. And we can verify that we still haven't changed the value of the actual number. 200 plus 90 is 290, plus 11 is still 301. Now what was neat about this is now appear all of these numbers are larger than the corresponding number in the same place. So we're ready to subtract. 11 minus 4 is... (Let's see. 10 minus 3 is 7 so...) 11 minus 4 is 7. 9 minus 6 is 3. And 2 minus 1 is 1. So we are left with 137.