We used to play the "24" game in 5th grade. The premise is you get 4 numbers 1-9 and have to combine them in some manner to get to the number 24. e.g. 6, 6, 6, 6 would be 6+6+6+6, or 2634 could be 2*6+3*4.

The one we could never solve was something like 7,7,8,9