Quickly multiply up to 20x20

I will assume that you know your multiplication table reasonably well up to 10x10.

Try this:

    * 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.