Estimating Sums and Differences by Rounding
This Grade 4 Eureka Math skill teaches students to estimate sums and differences of multi-digit numbers by rounding each number to a specified place value and then computing the approximate result. For example, to estimate 52,187 + 39,604 to the nearest ten thousand, round each: 50,000 + 40,000 = 90,000. For subtraction, 74,826 minus 31,145 rounds to 70,000 minus 30,000 = 40,000. The result is recorded with the approximately-equal symbol. This estimation skill from Chapter 3 of Eureka Math Grade 4 supports number sense and reasonableness checking.
Key Concepts
To estimate a sum or difference, first round each number to a specified place value, then perform the addition or subtraction on the rounded numbers. The result is an approximation, denoted by the $\approx$ symbol. For numbers $A$ and $B$, an estimated sum is $\text{round}(A) + \text{round}(B)$ and an estimated difference is $\text{round}(A) \text{round}(B)$.
Common Questions
How do you estimate a sum by rounding?
Round each addend to the specified place value, then add the rounded numbers. For 52,187 + 39,604 to the nearest ten thousand: 50,000 + 40,000 = 90,000.
How do you estimate a difference by rounding?
Round each number to the specified place value, then subtract. For 74,826 minus 31,145 to nearest ten thousand: 70,000 minus 30,000 = 40,000.
What symbol do you use to show an estimate?
Use the approximately equal symbol to show the result is an approximation, not exact.
When would you round to the nearest thousand instead of ten thousand?
When the numbers are smaller (in the thousands range) or when you need a more precise estimate. The place value you round to depends on the problem context.
How is estimating different from exact computation?
An exact computation gives a precise answer by following arithmetic rules. An estimate gives a close approximation using rounded values, which is faster and useful for checking reasonableness.