Mr. Someone has 2/3 of a package of ammunition for his hunting trip. When he comes back, he's only used 1/6 of it. How much is left?
2/3 - U = 1/6 where U is the fractional part used
Rearrange as
2/3 - 1/6 = U
4/6 - 1/6 = U
3/6 = U
1/2 = U ⇒ 1/2 of the package used
