the+answer+is

[[image:the_answer_is.jpg width="280" height="210" align="right"]]The answer is...
Split the class into groups. Challenge them to take turns to come up with a sum to which the answer is ...

Increase the challenge by
 * giving each group a time limit
 * scoring their sums based on level of difficulty, eg include a square number etc
 * penalty for incorrect sums
 * penalty for repeating a sum
 * bonus for a team spotting an incorrect sum

Alternatively, rather than scoring, give each team three lives and they lose one for every error or gain one for spotting someone else's error first.

Other examples include the answer being; 3x, 12cm, -21, etc (see powerpoint)