In just FIVE minutes you should learn to quickly multiply up to 20x20 in your 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.

• Take 15 x 13 for an example.
• Always place the larger number of the two on top in your mind.
• Then draw the shape of Africa mentally so it covers the 15 and the 3 from the 13 below. Those covered numbers are all you need.
• First add 15 + 3 = 18
• Add a zero behind it (multiply by 10) to get 180.
• Multiply the covered lower 3 x the single digit above it the "5" (3x5= 15)
• Add 180 + 15 = 195.

Squaring a repeating 6-digit number

1. Choose a number with repeating 6's .
2. The square is made up of:
   • One less 4 than there are digits in the number;
   • One 3;
   • The same number of 5's as 4's;
   • A final 6.

   Example:

1. If the number to be squared is 666:
2. The square has:
   one less 4 than digits in
   the number                 4 4
one 3                             3
same number of 5's as 4's           5 5
a final 6                               6
3. So the square of 666 is 443556.

1. If the number to be squared is 66666:
2. The square has:
   one less 4 than digits in
   the number)                 4 4 4 4
one 3                                  3
same number of 5's as 4's                5 5 5 5
a final 6                                        6
3. So the square of 66666 is 4444355556