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).

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).