How to Round Numbers Up and Down

Rounding numbers makes long numbers easier to work with. To round a two-digit number to the nearest ten, simply increase it or decrease it to the nearest number that ends in 0:

  • When a number ends in 1, 2, 3, or 4, bring it down; in other words, keep the tens digit the same and turn the ones digit into a 0.

  • When a number ends in 5, 6, 7, 8, or 9, bring it up; add 1 to the tens digit and turn the ones digit into a 0.

To round a number with more than two digits to the nearest ten, use the same method, focusing only on the ones and tens digits.

After you understand how to round a number to the nearest ten, rounding a number to the nearest hundred, thousand, or beyond is easy. Focus only on two digits: The digit in the place you’re rounding to and the digit to its immediate right, which tells you whether to round up or down. All the digits to the right of the number you’re rounding to change to 0s.

Occasionally when you’re rounding a number up, a small change to the ones and tens digits affects the other digits. This is a lot like when the odometer in your car rolls a bunch of 9s over to 0s, such as when you go from 11,999 miles to 12,000 miles.

Sample questions

  1. Round the numbers 31, 58, and 95 to the nearest ten.

    30, 60, and 100.

    The number 31 ends in 1, so round it down.

    The number 58 ends in 8, so round it up.

    The number 95 ends in 5, so round it up.

  2. Round the numbers 742, 3,820, and 61,225 to the nearest ten.

    740, 3,820, and 61,230.

    The number 742 ends in 2, so round it down.

    The number 3,820 already ends in 0, so no rounding is needed.

    The number 61,225 ends in 5, so round it up.

Practice questions

  1. Round these two-digit numbers to the nearest ten:

    a. 29
    b. 43
    c. 75
    d. 95
  2. Round these numbers to the nearest ten:

    a. 164
    b. 765
    c. 1,989
    d. 9,999,995
  3. Round these numbers to the nearest hundred:

    a. 439
    b. 562
    c. 2,950
    d. 109,974
  4. Round these numbers to the nearest thousand:

    a. 5,280
    b. 77,777
    c. 1,234,567
    d. 1,899,999

The following are the answers to the practice questions:

  1. Round to the nearest ten:

    a. 29 → 30. The ones digit is 9, so round up.
    b. 43 → 40. The ones digit is 3, so round down.
    c. 75 → 80. The ones digit is 5, so round up.
    d. 95 → 100. The ones digit is 5, so round up, rolling 9 over.
  2. Round to the nearest ten:

    a. 164 160. The ones digit is 4, so round down.
    b. 765 770. The ones digit is 5, so round up.
    c. 1,989 1,990. The ones digit is 9, so round up.
    d. 9,999,995 10,000,000. The ones digit is 5, so round up, rolling all of the 9s over.
  3. Focus on the hundreds and tens digits to round to the nearest hundred.

    a. 439 400. The tens digit is 3, so round down.
    b. 562 600. The tens digit is 6, so round up.
    c. 2,950 3,000. The tens digit is 5, so round up.
    d. 109,974 110,000. The tens digit is 7, so round up, rolling over all the 9s.
  4. Focus on the thousands and hundreds digits to round to the nearest thousand.

    a. 5,280 5,000. The hundreds digit is 2, so round down.
    b. 77,777 78,000. The hundreds digit is 7, so round up.
    c. 1,234,567 1,235,000. The hundreds digit is 5, so round up.
    d. 1,899,999 1,900,000. The hundreds digit is 9, so round up, rolling over all the 9s to the left.
  • Add a Comment
  • Print
  • Share
blog comments powered by Disqus
Advertisement

Inside Dummies.com