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Estimate sums using rounding

Estimation of whole-number sums involves using place value to round addends to a specified place—such as the nearest ten, hundred, or thousand—then adding the rounded values to obtain a reasonable approximation. The estimate reflects the size of the exact sum and supports checking whether a calculated answer is sensible; it does not require exact results, decimals, or generalized error analysis beyond these place-value rounding cases.

Detailed Explanation: Estimate sums using rounding

To estimate a sum, round each addend to the specified place. Then add the rounded numbers.

Remember:

  • Look at the digit immediately to the right of the place you are rounding to.
  • If that digit is 55 or greater, round up.
  • If it is less than 55, keep the rounding digit the same.
  • Change the digits to the right into zeros.

Example: Estimate 3,746+2,1893{,}746+2{,}189 to the nearest hundred.

  1. Round 3,7463{,}746 to the nearest hundred. The tens digit is 44, so round down:
3,746≈3,7003{,}746\approx 3{,}700
  1. Round 2,1892{,}189 to the nearest hundred. The tens digit is 88, so round up:
2,189≈2,2002{,}189\approx 2{,}200
  1. Add the rounded numbers:
3,700+2,200=5,9003{,}700+2{,}200=5{,}900

So, the estimated sum is:

5,900\boxed{5{,}900}

Learn by doing: Estimate sums using rounding

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    Addition - Estimate Sum - 2 & 2 Digit

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