The Main Difference Between Mental Computation and Estimation or Rounding

Multiple Choice

The main difference between mental computation and estimation or rounding is:

A) mental computation is done before estimation or rounding is applied.
B) mental computation is easier to understand than estimation or rounding.
C) mental computation gives exact answers while estimation or rounding only gives approximate answers.
D) mental computation is preferred by teachers over estimation or rounding because it is easier to grade since there is only one right answer.