500
If the principal eats 2/4 of the cake, the Coach eats 1/4 of the cake, how much does the Music teacher have to eat to finish it off? (Make it all gone!)
Start with a whole, 4/4. Principal: 4/4 - 2/4 = 2/4, Coach has 2/4 - 1/4 = 1/4. There is 1/4 of the cake left. So the Music teacher has to eat 1/4 of the cake to leave nothing but crumbs left.