Yeah, this one is sums.
One of them was twice the age of the other two years ago, but now they're twins.

Or something.
( Dr Preference AjcuiVd289, Mon 18 May 2009, 0:13, archived)

1. 1+1
2. 1+2
3. 2+2
4. 2+3
5. 3+3
6. 3+4
7. 4+4
8. 4+5
9. 5+5
10. 5+6

The clever bit is that you don't even have to calculate the answers yourself when checking! It's always the number of the next question. Apart from number 10. I haven't worked that one out yet.
(MooCow_Byter, Mon 18 May 2009, 0:16, archived)

11.

( Dr Preference AjcuiVd289, Mon 18 May 2009, 0:18, archived)