Discuss once again with the students that it is important to be able to multiply by 10, so that you can calculate how many you have if you have 10 a certain number of times. Ask how they can calculate a multiplication problem with 10 and have them solve a few problems with multiplying by 10. Then practice multiplying with 10 by sitting in a circle and throwing a ball, during which you name a multiplication problem with the number 10. The student catches the ball, states the answer, and throws it to the next student. Unless the forbidden number is in the answer. This is, to start, the number 2. Then you only throw the ball and do not answer. If you do give the answer, then you're out of the game. To make the game more difficult, you can discuss adding more than one forbidden number.