Arthur's Funny Money, by Lillian Hoban. New York: Harper & Row. 64 pp. $7 .25.

This is literally a book about monkey business. Arthur, an endearing chimpanzee hero, sets up a business washing bikes, and troubles ensue. Lillian Hoban, author and illustrator for this and other Arthur stories in the ''I Can Read'' series, unobtrusively incorporates a mathematics lesson into the text, with humor to enliven the story, but she doesn't obscure the point: Arthur's real difficulty is that he hasn't learned math, and as a result is cheated by his friends.

Children will enjoy spotting the flaws in Arthur's business negotiations as they cheer him on to final success. Arthur and the readers, meanwhile, learn about the intricacies of selling and the value of truth in advertising.