Use "7" as your "Key"

Try this trick for multiplying two 2 digit numbers under 20. For example...

First off, make sure the larger number is on top.

Then think of the number 7. Well, the shape of it, anyway.

Now ADD 13 and 2 and stick a zero on the end.

Now cover up everything in the left (or 10's) column.

Now ADD 150 and 6 and you get 156

Done!