x, y, and z are all unique numbers. If x is chosen randomly from the set {10, 11} and y and z are chosen randomly from the set {20, 21, 22, 23}, what is the probability that x and y are prime and z is not?
Choose the correct choice from the following options.
A) 1 / 5	B) 3 / 20	C) 1 / 8	D) 3 / 10	E) 1 / 10

Rationale: p ( x is prime ) = 1 / 2 p ( y is prime ) = 1 / 4 if y is prime , then z is not prime since y and z are unique . then the probability is 1 / 2 * 1 / 4 = 1 / 8 the answer is c .
Answer: C