This is pretty hard for a 4th grader but if you practice you can do it. I teach maths in high school and I sometimes see kids of 15 or 16 who can't do simple multiplication. Keep practicing! Hint: After you click the chips, forget the mouse. Use the keypad and the enter button. Good luck!
This is the same as Retrosnob's but it does not go up to 12 C:
