In a race where 18 cars are running, the chance that car X will win is 1/8, that Y will win is 1/12 and that Z will win is 1/6. Assuming that a dead heat is impossible, find the chance that one of them will win. Choose the correct answer:
A) 1 / 140
B) 1 / 180
C) 3 / 12
D) 3 / 8
E) 57 / 120

Rationale: "required probability = p ( x ) + p ( y ) + p ( z ) ( all the events are mutually exclusive ) . = 1 / 8 + 1 / 12 + 1 / 6 = 3 / 8 answer : d"
Answer: D