[dpwm]

I was actually taught this in a small village primary school as a way to remember the 9 times table up to 90. I think we were also taught how to apply it quickly: If you want n * 9, the first digit is n - 1 and the second is 9 - (n - 1).

Of course, it fails at 99. It wasn't until much later that I learnt that all multiples of 9 have the property of their digits adding up to multiples of 9 and that there exist proofs.

[superflyguy]

An easy way of lower multiples of nine is to hold your hands in front of you, and if you want to work out, say, 4 times 9 put down your forth finger and look at the number of fingers on each side of that finger...