Estimating sums and differences of decimals means finding an answer that is close to the exact amount. You use rounding to make the numbers easier to work with before adding or subtracting.
Estimation helps you check if your exact answer makes sense. It’s a quick way to see if your result is reasonable.
To round a decimal, look at the digit to the right of the place value you are rounding to. If it is 5 or greater, round up. If it is 4 or less, keep the digit the same.
Decide which place value makes sense to round to—tenths, hundredths, or whole numbers—depending on the problem.
When estimating a sum, round each decimal to the same place value, then add the rounded numbers to get an approximate total.
Your estimated sum should be close to the exact sum but easier to calculate mentally.
When estimating a difference, round each decimal to the same place value, then subtract the rounded numbers.
Estimation helps you check if your subtraction answer is reasonable. If your exact answer is very different, recheck your work.
Estimation is useful when you do not need an exact answer or when you want to check if your result makes sense. It helps you make quick, smart decisions in everyday math situations.
Use estimation to check if an answer is reasonable before or after doing exact calculations.