Limit needed on play time

I love this app but.... Every time my child completes the math he can play the fun part of the game indefinitely . There isnt any incentive to do more math. I would like it if there was a way for parents to limit the fun part of the game to 2 tries for each set of math problems completed. I think this change would motivate my son to do more math.

Mikey From AZ about Math Bingo, v1.7