2 digit multiplication trick under 20

schoolash.blog - Can you calculate the multiplication below each within 5 seconds without using a calculator?

18 x 12

12 x 17

16 x 18

13 x 17

You do was wonder if all the above calculations can be completed each within 5 seconds.

This is not magic but we can do so by the following process:

Example -> Looking for the 18 x 12

- Total the first two digits (18) with the last digit number into two (2)

----------------------------> 18 + 2 = 2 0

- Multiply the last digit is 8 x 2 = 1 6
- Then the final result is =

2_0
__1_6
------------ +
216

How?
Does the above explanation can already be understood?

We try searching some other values ​​such as -> 14 x16

- Total the first two digits (14) with the last digit number into two (6)
-> 14 +6 = 2 0
-Multiply the last digit ie = 4x6 = 2 4
- So the end result =

2_0
__2_4
--------- +
224

Still confused?

Take it easy.

We'll try again with the following multiplication -> 13 x 15

- Total the first two digits (13) with the last digit number into two (5)
-> 13 + 5 = 1 8
-Multiply the last digit ie = 3x5 = 1 5
- So the end result =

1_8
__1_5
---------- +
195