A lesson on estimation - add/subtract 4-digit numbers (3rd grade math)
In this math lesson, we first estimate the result of addition / subtraction problems by rounding the numbers to the nearest hundred and adding/subtracting mentally. I also calculate the exact result, and then we compare.
In the last exercise, the viewer gets to be a "teacher-detective" and to find out why the student's subtraction is incorrect.
See also
The connection with addition and subtraction
Math Mammoth Grade 3 curriculum