Multiplying teen numbers (between 11 and 19) together in Head

With this trick, you will be able to multiply any two numbers from 11 to 19 in your head quickly, without the use of a calculator.

Step 1:   Multiply the unit digit of both numbers and write down the ones; carry, if any. This gives the one’s digit of the answer.

Step 2:   Add the unit digit of the smaller number (preferable) to the whole number of larger number (or vice versa) and add carried digit. Write it down.

Take 15 x 13 for an example.

• Multiply 5 by 3 to get 15; write 5, carry 1.
• Add 3 to 15 to get 18; add 1 getting 19. Write 19.

So, 15 x 13 = 195

Let’s try another example:

17 x 18 =?

Step 1:  8 x 7 = 56; write 6, carry 5.

Step 2:  18 + 7 = 25; 25+5 = 30; write 30.

So, 17 x 18 = 306