With mental math tricks you will be able to work out sums in your head more rapidly – a critical skill in math. Here are examples of some mental math strategies for addition.
Break Up the Numbers Strategy
This strategy is used when regrouping is required. One of the addends is broken up into its expanded form and added in parts to the other addend. For example:
can be calculated this way:
Front-End Strategy
This strategy involves adding the front-end digits - the hundreds, then the tens and then the ones. For example:
Front-End Estimation
This method involves adding from the left and then grouping the numbers in order to adjust the estimate. For example:
Compatible Number Strategy
Compatible numbers are number pairs that go together to make “friendly” numbers. That is, numbers that are easy to work with. For example:
Near Compatible Estimation
Knowledge of the compatible numbers that are used for mental calculations is used for estimation. For example:
Balancing Strategy
A variation of the compatible number strategy, this method involves taking one or more from one addend and adding it to the other. For example, 68 + 57 becomes 70 + 55 (add 2 to 68 and take 2 from 57).
Clustering in Estimation
Clustering involves grouping addends and determining the average. For example:
when estimating 53 + 47 + 48 + 58 +52, notice that the addends cluster around 50. The estimate would be 250 (5 x 50)
Special Tens Strategy
In the early grades, students learn the number of pairs that total ten – 1 and 9, 2 and 8, 3 and 7, and so on. These can be extended to such combinations as 10 and 90, 300 and 700, etc.
Compensation Strategy
Using the compensation strategy, you substitute a compatible number for one of the numbers so that you can more easily compute mentally. For example, in doing the calculation 47 + 29 one might think (47 + 30) – 1.
