Mental Math Grade 6 Teacher's Guide

In mathematics, it is essential that estimation strategies are used by
students before attempting pencil/paper or calculator computations to help
them determine whether or not their answers are reasonable. When
teaching estimation strategies, it is important to use words and phrases
such as, about, almost, between, approximately, a little more than, a little
less than, close to and near.
Rounding in Addition and Subtraction
In mathematics, it is essential that estimation
strategies are used by students before
attempting pencil/paper or calculator
computations to help them determine whether or
not their answers are reasonable.
Nearly all computational estimations involve
replacing or substituting difficult-to-handle
numbers with number that can be more easily
dealt with mentally.
With this strategy for addition and subtraction, you start with the highest
place values in each number, round them to the closest 10, 100 or 1000,
and then add or subtract the rounded numbers.
Examples
a) To estimate 378 + 230, think, “378 rounds to 400 and 230 rounds to
200; so, 400 plus 200 is 600.”
b) To estimate 4276 + 3937, think, “4276 rounds to 4000 and 3937
rounds to 4000, so 4000 plus 4000 is 8000.”
c) To estimate 594 - 203, think, “594 rounds to 600 and 203 rounds to
200, so 600 subtract 200 is 400.”
d) To estimate 6237 – 2945, think, “6237 rounds to 6000 and 2945
rounds to 3000, so 6000 subtract 3000 is 3000.”
52 Mental Math – Grade 6