Use estimation to predict the sum and or difference between two 2-digit numbers in a problem-solving situation...

by estimating the sum of two 2-digit numerals by using tens.
to estimate the sum of 43 + 56, use 40 + 50 (the sum is close to 90).

Thinking BlocksPart Part WholeSum and Difference


by estimating the difference of two 2-digit numerals by using tens.
to estimate the difference of 56 - 23, use 50 - 20 (the difference is close to 30).

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