BrainQX is a puzzle that tests your arithmetic skills. A grid is generated with some cells blank and some containing numbers. The aim is to clear the grid by placing a number on a blank cell, such that the last digit of the surrounding cells matches the placed number. Three numbers are provided to choose from. Once you get the hang of it, it becomes a matter of how quickly you can eliminate the numbers! Your timings are recorded so that you can monitor your progress.