This is a quick way to practice addition or multiplication.
Have two students face each other. They put their hands behind their backs. On the count of three both partners put up some fingers. Either add or multiply the number of fingures put up by each partner. The one to give the answer first is the winner. They already know what number they are putting up so they just have to add it or multiply it by the number thier partner puts up. This can last only a few min. or as long as you like it to last.