How to Round Whole Numbers

How to Round Whole Numbers
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  • 0:05 Rounding Whole Numbers
  • 0:35 To the Nearest Tens
  • 2:33 To the Nearest Hundreds
  • 4:02 Example
  • 4:46 Lesson Summary
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Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

View this lesson to learn how you can round whole numbers. Practice rounding to the nearest tens and hundreds. Learn which digit you need to look at to know whether to round up or down.

Rounding Whole Numbers

When you are solving math problems, it can sometimes be much easier to solve your problem when you round your numbers. For example, it is easier to solve 10 * 40, than it is to solve 13 * 42. To round means to replace a number with an approximate and more simple number.

Because rounding is an important skill to have, in this lesson, we will look at rounding to the nearest tens and to the nearest hundreds. Rounding can help you in real life, like when you are at the store and you need to quickly figure out about how much you will need to pay.

To the Nearest Tens

For example, you might be at the toy store where you want to purchase three games. The games are priced at $17, $21, and $26. About how much will you be spending for those three games? While you could go ahead and perform the addition of 17 + 21 + 26, you could also round these numbers to the nearest tens so that you can quickly perform the addition perhaps in your head. To round to the nearest tens means to round your number so that your last non-zero digit is in the tens place, and you have a 0 in the ones place.

To perform this rounding, you will look at the digit that is in the ones place. This will tell you whether you need to round your digit in the tens place up or down. If the digit in the ones place is less than 5, then you round down by keeping your digit in the tens place the same and then changing the ones digit to 0. If the digits in the ones place is 5 or greater, then you round up by adding 1 to the digit in the tens place and then changing the ones digit to 0.

So, the 17 rounds up to 20 because the digit in the ones place, 7, is 5 or greater. We round up by adding 1 to the digit in the tens place, the 1. So 1 + 1 is 2, and we change the ones digit to a 0. We get 20. What about the 21? Do we round up or down? That's right, we round down because the digit in the ones place is less than 5. What do we do with the 2 that is in the tens place? Right again, we keep it the same. 21 rounded to the nearest tens is then 20. What about 26? Well, 6 is greater than 5, so we round up. So, 26 rounded to the nearest tens is 30.

Now that we've rounded these numbers, we can easily add them up. 20 + 20 + 30 is equal to 40 + 30 = 70. Wasn't this much easier to do than 17 + 21 + 26? According to the rounded numbers, you will be spending around $70 to purchase those three games.

To the Nearest Hundreds

If the numbers you are dealing with are larger, you will need to look at a different digit to determine whether you need to round up or round down. For example, if your number has three digits, then you could round to the nearest hundreds to make your problem easier to solve. Rounding to the nearest hundreds means to round your number so that your last non-zero digit is in the hundreds place, and you have a 0 in the tens and ones place.

Let's say that you and your friend have both won the lottery. You won $634 and your friend won $289. If you both round these numbers to the hundreds place, you would be able to quickly add up the total of your winnings together. To round to the nearest hundreds, you will look at the digit in the tens place. If this digit is less than 5, then you round down by keeping the digit in the hundreds place the same and changing the tens and ones digit to 0. If the tens place digit is 5 or greater, then you round up by adding 1 to the hundreds place digit and changing the tens and ones digits to 0.

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