Mike and his little brother, Andy, are headed for the Dinosaur Card Trading Fair. They're ready to wheel and deal. It's, 4 Stegosaurus for 1 Triceratops and 2 Triceratops for 1 Allosaurus. But can they get what they really want: The tremendous, gigantic, ferocious, Tyrannosaurus rex? The Math concept of equivalency - understanding when values are equal ??? is introduced in this fast-paced story as two brothers try to beat the clock and make the ultimate trade.