One thing that's interested me over the years was the childhood realisation that the nine times table "went up" one side, and "came down" the other.

It wasn't until I grew up and started trying to think about problems from different points of view that I stumbled across the fact that this situation is true for all number bases.

so, in hexadecimal, if you take the nine as being ten-1, the F times table looks much like the nine times table you had as a kid.

1 x F = F

2 x F = 1E

3 x F = 2D

4 x F = 3C

5 x F = 4B

6 x F = 5A

7 x F = 69

8 x F = 78

9 x F = 87

A x F = 96

B x F = A5

C x F = B4

D x F = C3

E x F = D2

F x F = E1

10 x F = F0

This can be quite a revelation for some people. Funnily enough, it works right down to binary.

1 x 1 = 1

10 x 1 = 10

okay, that was a poor maths joke, so now I'll just get my coat.