Addition Mental Math Tricks | Mental Maths - Class 1 PDF Download

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:
57 + 38
can be calculated this way:
57 + 330 = 87
87 + 8 = 95

Front-End Strategy

This strategy involves adding the front-end digits  - the hundreds, then the tens and then the ones.
For example:
124 + 235
100 + 200 = 300
20 + 30 = 50
 4 + 5 = 9
300 + 50 + 9 = 359

Front-End Estimation

This method involves adding from the left and then grouping the numbers in order to adjust the estimate.  
For example:
2667 + 5239
2000 + 5000 = 7000
600 + 200 = 800
No, make that 900
As 39 + 67 is about 100
7000 + 900 = 7900

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:
25 + 78
Easier:
25 + 75 + 3 = 103

Near Compatible Estimation

Knowledge of the compatible numbers that are used for mental calculations is used for estimation.  
For example:
76 + 45 + 19 + 26 + 52
Estimating these numbers:
76 + 26 is about 100
45 + 52 is about 100
Add 19
Estimate answer, about 219

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).
68 + 57
Becomes
70 + 55 = 125
[Add 68 + 2 and 57 - 2]

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)
When estimating
53 + 47 + 57 + 52 + 48
The addends cluster around 50
5 x 50 = 250

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.
1 and 9
2 and 8
3 and 7
4 and 6
5 and 5
6 and 4
7 and 3
8 and 2
9 and 1

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.
47 + 29
[47 + 30] - 1 = 76