Simply add to ten to earn points in this puzzling game. The game board is a seven by seven grid. Click on an arrow to add every pair of numbers in any two rows or columns together. Those sums are then divided by ten and the remainder replaces each number in the yellow line. If the remainder is zero the number disappears and you earn some points. That is an example of modular arithmetic and it is as fun as it sounds. Play this game to learn more.