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D.1 Round to the nearest ten or hundred

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What is Rounding?

Rounding is a way of making numbers simpler while keeping their value close to what it was. We round numbers to the nearest ten, hundred, or other place value to make them easier to work with.

Examples:
  • 43 rounded to the nearest ten → 40
  • 276 rounded to the nearest hundred → 300
Note

Rounding makes numbers easier to read, estimate, and calculate with, but it is not the exact number.

Rules for Rounding

To round a number, find the place value you are rounding to, then look at the digit to the right of it.

Steps:
  • If the digit is 0, 1, 2, 3, or 4 → round down
  • If the digit is 5, 6, 7, 8, or 9 → round up
Note

Always keep the digits to the left of the rounding place the same, and change all digits to the right to zeros.

Rounding to the Nearest Ten

When rounding to the nearest ten, look at the ones place.

Examples:
  • 67 → 70 (ones digit 7 means round up)
  • 142 → 140 (ones digit 2 means round down)
  • 38,954 → 38,950 (ones digit 4 means round down)
Note

Only the ones place tells you whether to round up or down when rounding to the nearest ten.

Rounding to the Nearest Hundred

When rounding to the nearest hundred, look at the tens place.

Examples:
  • 276 → 300 (tens digit 7 means round up)
  • 432 → 400 (tens digit 3 means round down)
  • 85,649 → 85,600 (tens digit 4 means round down)
Note

Always check the tens place when rounding to the nearest hundred.

Why Do We Round Numbers?

Rounding helps us estimate quickly and work with simpler numbers in real life, like when shopping, measuring, or comparing values.

Examples in Real Life:
  • Estimating the total cost of items in a store
  • Finding about how many people are in a stadium
  • Measuring distances on a map
Note

Rounding is useful for estimation, but for exact answers you must use the original number.