A student committee on academic integrity has 30 ways to select a president and vice president from a group of candidates. The same person cannot be both president and vice president. How many candidates are there? Options:
A) 7	B) 8	C) 9	D) 6	E) 11

Rationale: "xc 1 * ( x - 1 ) c 1 = 30 x ^ 2 - x - 30 = 0 ( x - 6 ) ( x + 5 ) = 0 x = 6 , - 5 - 5 ca n ' t possible . d"
Answer: D