Here's a puzzle: Put two quarters side by side so the ridges mesh like gears, then hold one still and roll the other all the way around it. How many revolutions will George Washington make?
That's a riddle from Ethan Canin's new novel, A Doubter's Almanac. The book follows Milo Andret, a troubled math genius, through three generations of his family. Canin tells NPR's Ari Shapiro about his protagonist's Michigan childhood, and the answer to the book's two quarter puzzle.