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!