Estimate Sum and Differences - Whole Numbers Game

A high paced math game for Fourth Grade kids that would certainly help them in the long run. The game is all about estimating the sum or difference of an expression to its nearest tens or hundreds. For that, there is a flying ball with an expression and you need to land this flying expression in its nearest tens' or hundreds' field, making your way all through the flying sticks. If you crash into any, you lose a chance. Well, what could practically be more interesting a math game than this?