You choose the time and the number of questions. Can you beat the clock?

Level One
http://www.oswego.org/ocsd-web/games/SpeedGrid/Subtraction/urikasub1res....

Level Two
http://www.oswego.org/ocsd-web/games/SpeedGrid/Subtraction/urikasub2res....

Level Three
http://www.oswego.org/ocsd-web/games/SpeedGrid/Subtraction/urikasub3res....