a.) a/f = b/c b.) f/c = b/a c.) c/a = f/b d.) a/c = b/f e.) af/bc = 1/1 Cross multiply each one: a.) a/f = b/c ---> ac = bf b.) f/c = b/a ---> af = bc c.) c/a = f/b ---> bc = af d.) a/c = b/f ---> af = bc e.) af/bc = 1/1 ---> af = bc Obviously they're all the same except a.) Edwin