Multiplication with your fingers

Here is interesting trick to multiply numbers in second half of multiplcation table (6-10). I do not recall where I learned it from but it has been around for quite some time. Best way to explain how it works is on example:

to multiply 6 by 7 you open 1 finger on one hand (6-5 = 1) and 2 fingers on another (7-5 = 2), then you multiply number of closed fingers on your hands and add it to sum of open fingers multiplied by 10. In our case -

4 (closed fingers on one hand) x 3 (closed fingers on another hand) + (1 + 2) * 10 = 42

another example:

8*9 translates to : 2*1 + (3+4) * 10 = 72

:)