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Jun28

Mental Math by Association

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In this post, we are going to learn a mental math trick for adding and subtracting various numbers. It’s all about grouping the numbers that can give us exactly ten. In order to do so, we really need to pay attention to the numbers.

Mental Math: Addition

In order to add, we need to see if the problem we’re working on has any of these pairs:

1 + 9 = 10

2 + 8 = 10

3 + 7 = 10

4 + 6 = 10

5 + 5 = 10

6 + 4 = 10

7 + 3 = 10

8 + 2 = 10

9 + 1 = 10

For example:

5 + 6 + 5 + 1

If we look at the problem, we see 5 + 5 = 10. After, we only have to add the rest of the numbers: 10 + 6 + 1 = 17 

Let’s look at another example:

12 + 14 + 18

In this problem, we first add 12 + 18 = 30, and after 30 + 14 = 44

mental math

Mental Math: Subtraction

In order to subtract, we have to look for the numbers that give us exactly 10 when we subtract them.

For example:

16 – 4 – 6

First we subtract 16 – 6 = 10, and after 10 – 4 = 6

Let’s look at another example:

38 + 15 – 18

We’ll first subtract 38 – 18 = 20, and then add 20 + 15 = 35

mental math

By solving this way, we can add and subtract various numbers more easily. Also check out different strategies for mental calculation from Smartick!

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