If x, y, and z are positive integers and x = 4y = 7z, then the least possible value of x - y - z is
Pick one:  A) 33  B) 17  C) 49  D) 16  E) 23

Rationale: x - y - z = x - x / 4 - x / 7 = ( 28 - 7 - 4 ) x / 28 = 17 x / 28 17 is not divisible by 28 ( it ' s a prime # ) , so for least value , x = 28 answer - b
Answer: B