Let f(x,y) be defined as the remainder when (x–y)! is divided by x. If x=24, what is the maximum value of y for which f(x,y)=0?
Choose the correct option:
A) 12
B) 15
C) 18
D) 20
E) 21
The question is finding y such that (24-y)! is a multiple of 24. That means we need to have 2^3*3 in (24-y)!   4! is the smallest factorial number with 2^3*3 as a factor.   24-y = 4   y = 20   The answer is 20.
<result>D</result>
Let f(x,y) be defined as the remainder when (x–y)! is divided by x. If x=24, what is the maximum value of y for which f(x,y)=0?