Current time:0:00Total duration:6:17
0 energy points

Rounding to nearest 10 and 100

Learn to round up to 4-digit numbers to the nearest ten and hundred. Created by Sal Khan.
Video transcript
We've got four numbers here. What I want to do is try to round each of these to the nearest 10 and to the nearest hundred. So I encourage you to pause the video and try that right now. So let's make two columns. Let's make one first for the nearest 10 and then make another column for the nearest 100. And let's start with 154. So 154, what is the multiple of 10 above 154? Well, it's 160. And the multiple of 10 below 154 is 150. So we're going to round up to 160 or down to 150. Well, when we're rounding to the nearest 10, we need to look at the ones place. One place to the right of the place that we're rounding. So we look at this 4 in the ones place. Since 4 is less than 5, we round down to 150. Now, let's think about that same number, rounding to the nearest hundred, so 154 to the nearest hundred. So now we need to think about if we were to round up, what's the multiple of 100 above 154? 160 isn't the multiple of 100 The multiple of 100 above 154 is 200. What's the multiple of 100 below 154? Well, that's going to be 100. So if we're going to round to the nearest hundred-- so we look at the hundreds place. We'll look one place to the right of that, which is the tens place. If that place is 5 or greater, we round up. If it's less than 5, we round down. Well, this is clearly 5 or greater so we round up. So this is interesting. When we rounded to the nearest 10, since we had a 4 in the ones place, we rounded down. But when rounded to the nearest hundreds, since we had a 5 in the tens place, we rounded up to 200. Let's do some more of these. This is fun. So 4,674. The multiple of 10 above that is 4,680. The multiple of 10 below that, 4,670. Remember, we're concerned only with the multiple of 10. So do we round up or down? Well, we're thinking about rounding the tens place. So that's why it's either going to be an 8 if we round up, or a 7 if we round down. To figure that out, we look at the ones place. If the ones place is 5 or greater, we round up. If it's less than 5, we round down. It's, once again, less than 5, so we round down to 4,670. Now let's round the same number to the nearest hundred. What's the multiple of 100 below this? Well, the multiple of 100 below this is 4,600. The multiple of 100 above this is 4,700. If we're trying to think about rounding to the nearest hundred, we want to look at the tens place. The tens place is 5 or greater, so we round up to 4,700. Now let's tackle 9,995. And once again, always try to pause these, if you haven't done so already, to try to do this on your own. So 9,995. What is the multiple of 10 below this. Well the multiples of 10 below this is 9,990. And what's the multiple of 10 above this? Well, if you increase this by 10, you actually get to 10,000. So you might say, hey, well isn't this a multiple of 100, and actually this is a multiple of a thousand-- it's also a multiple of 10,000. It's all of those, but the multiple of 10 right above 9,995 is 10,000. You just have to add a little bit to this to get to 10,000. Or the multiple of 10 below it is clearly 9,990. 10 more than that gets you to 10,000. So how do we around this? Well, once again, if we're rounding to the nearest 10, we want to look at the ones place. The ones place is 5 or greater so we round up to 10,000. Now, let's round to the nearest hundreds. You should be getting used to this now. To the nearest hundreds, what is the hundreds below this? Well, it's 9,900. What is 100 above this, the next multiple of 100 above this? Well, if you add 100 to 9,900 you once again get 10,000. So how do we decide whether to round up or down? Well, we don't look at the ones place anymore. We're now rounding to the nearest hundred. So we want to round to the nearest hundred. To do that, we look one place to the right, which is the tens place. If this is 5 or greater, we round up. If it's less than 5, we round down. It is 5 or greater so once again we round up to 10,000. Now we have one more, 8,346. The multiple of 10 below it is 8,340. Multiple of 10 above that is 8,350. If we're going to round to the nearest 10, we need to look at the ones place. The ones place is 5 or greater, so we round up. Now, let's round to the nearest hundred. 8,346, the multiple of 100 above this is 8,400. The multiple of 100 below this is 8,300. Notice we're rounding to the nearest hundreds. If we were to round up, the hundreds place becomes a 4. If we round down, the hundreds place stays at 3, but it's followed by zeroes. If we want to round to the nearest hundreds, we need to look at the tens place. The tens place here is less than 5, so we round down to 8,300. Notice, again, when we round to the nearest tens, we rounded up to 8,350. When we round to the nearest hundreds, we rounded down to 8,300.