In the siblings' latest adventure, their grandmother is having a birthday (again! see Bunny Cakes, p. 67), so Ruby takes Max shopping. A music box with skating ballerinas is Ruby's idea of the perfect present; Max favors a set of plastic vampire teeth. Ruby's $15 goes fast, and somehow, most of it is spent on Max. The music box of Ruby's dreams costs $100, so she settles for musical earrings instead. There isn't even a dollar left for the bus, so Max digs out his lucky quarter and phones Grandma, who drives them home--happily wearing her new earrings and vampire teeth. As ever, Wells's sympathies are with the underdog: Max, in one-word sentences, out-maneuvers his officious sister once again. Most six-year-olds will be able to do the mental subtraction necessary to keep track of Ruby's money, and Wells helps by illustrating the wallet and its dwindling contents at the bottom of each page where a transaction occurs. Younger children may need to follow the author's suggestion and have an adult photocopy the ""bunny money"" on the endpapers, so they can count it out. Either way, the book is a great adjunct to primary-grade math lessons.