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E.1 Estimate sums by rounding numbers - up to 1,000

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What is estimation?

Estimation is finding an answer that is close to the exact amount. It helps us make quick calculations without solving a problem exactly.

Example:
  • If the exact answer is 248 + 363, you can round and estimate to find an answer that is close.
Note

Estimation does not give the exact answer, but it helps check if your exact answer makes sense.

How to identify when to estimate

You should use estimation when the problem asks for an approximate answer or when checking if your exact answer is reasonable.

Clues to estimate:
  • Words like about, around, or approximately.
  • When numbers are large and an exact answer is not needed quickly.
  • When you want to check if your exact calculation makes sense.
Note

Estimation is especially helpful in real life, such as shopping, traveling, or solving word problems.

How to round numbers

Rounding means changing a number to the nearest ten or hundred to make it easier to work with.

Steps to round:
  • Find the place value you are rounding to (tens or hundreds).
  • Look at the digit to the right.
  • If the digit is 5 or greater, round up. If it is 4 or less, round down.
Note

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

Estimating sums by rounding

To estimate a sum, round each number to the nearest ten or hundred, then add the rounded numbers together.

Examples:
  • 248 + 363 → Round to nearest ten: 250 + 360 = 610 (estimate)
  • 427 + 589 → Round to nearest hundred: 400 + 600 = 1,000 (estimate)
  • 672 + 318 → Round to nearest ten: 670 + 320 = 990 (estimate)
Note

The estimated sum should be close to the exact sum, but it will be easier to calculate in your head.

Why estimation is important

Estimation helps you check your work, solve problems faster, and decide if your answer makes sense.

Example:
  • If a store receipt shows $248 + $363 = $1,248, you can quickly estimate 250 + 360 = about $610. The receipt is wrong, and estimation helped you notice!
Note

Estimation is a powerful tool for problem solving in school and everyday life.