Memorization of the multiplication facts is fun and easy with this colorful and clever book of cartoons and stories. Children learn to associate the numbers with the characters in the story. To teach 4x4, the story tells about Bart who loves to go hang gliding and can"t wait until he turns 16 so he can get his driver"s license and drive his 4 by 4. Children easily remember once the story is learned. The caption below the story says: Remember: you have to be 16 to drive a 4x4. There are cartoons and stories for all the difficult facts, ie. the 3"s, 4"s, 6"s, 7"s, and 8"s. Tricks are are used to teach the easier ones ie. 1"s, 2"s, 5"s, and 9"s. Kids love the stories and will never forget "You have to be 16 to drive a 4 by 4, (4x4). Over 500,000 copies have been sold to schools in the US since 1992.