A student committee on academic integrity has 56 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? Choose the correct option:  A) 7  B) 8  C) 9  D) 10  E) 11

Rationale: xc 1 * ( x - 1 ) c 1 = 56 x ^ 2 - x - 56 = 0 ( x - 8 ) ( x + 7 ) = 0 x = 8 , - 7 - 7 ca n ' t possible . hence 8 should be the answer b
Answer: B