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A Faster Way to Multiply Numbers between 11×11 to 19×19

At Singapore, primary students learn multiplication table of 1 to 10. For larger number, they tend to use calculator. Why not we let our brains “exercise” so that we can have “healthier” brains?

In this post, a simple multiplication method for numbers between 11×11 to 19×19 is shown. It is believed that this method originated from India. I hope that our Indian friends would not mind to share.

Calculate 11 x 15 without using calculator:

Step 1

Add 11 to the digit of the second number, 5.

11 + 5 = 16

Step 2

Multiply 10 to the number from Step 1.

16 x 10 = 160

Step 3

Multiply the digit of the first number, 1 and the digit of the second number, 5.

1 x 5 = 5

Step 4

Add the number from Step 2 and Step 3.

160 + 5 = 165

Thus, 11 x 15 = 165

Do you find this amazing?

Let’s try a second example: 12 x 17

(a) 12 + 7 = 19

(b) 19 x 10 = 190

(c) 2 x 7 = 14

(d) 190 + 14 = 204

A third example: 18 x 18

(a) 18 + 8 = 26

(b) 26 x 10 = 260

(c) 8 x 8 = 64

(d) 260 + 64 = 324

The method is faster and easier than the conventional method. You may want to try out other numbers and see for yourself. Have fun!