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3rd Grade Math
12. 3.NBT.A.3
12.2 Addition using Estimation
Addition Using Estimation
Round numbers to the nearest ten or hundred, add the rounded values, and use the estimate to check if an exact sum is reasonable.
What You'll Learn
Round each addend to the nearest ten or hundred before adding to get a quick estimate
Apply the rounding rule by checking the digit right of the rounding place to round up or down
Add the rounded numbers, for example \( 20 + 40 = 60 \), to estimate the sum
Compare an estimate to the exact sum to decide whether the exact answer is reasonable
Recognize that a good estimate is close to, but simpler than, the exact total
What You'll Practice
1
Rounding two-digit and three-digit numbers before adding
2
Estimating sums of numbers up to 1000
3
Using mental math to calculate approximate totals
Why This Matters
Estimation helps you quickly check if answers make sense, make fast decisions when shopping or budgeting, and solve problems when exact calculations aren't needed. This mental math skill builds number sense you'll use daily throughout your life.
This Unit Includes
4 Video lessons
Practice exercises
Learning resources
Skills
Estimation
Rounding
Addition
Mental Math
Number Sense
Place Value
OH Curriculum Aligned