Which is heavier, a pound of gold or a pound of feathers?"" Everyone we asked was flummoxed by this one; the answer is not elementary physics. Others of the 108 puzzlers require not only more or less deep thought but often paper, pencil and scissors; they comprise a variety of mental, mathematical and manipulative exercises. Our juvenile testers recognized only a few although many follow standard patterns. The layout is inviting, the sketches snappy; best of all, if you're a dodo with one, you can be a wizard with the next.