If 21!/3^x is an integer, what is the greatest possible value of x?  Answers: A) 3 B) 4 C) 5 D) D E) 7
21 - 7 *3   18 - 3*3*2   15 - 5*3   12 - 4*3   9 - 3*3   6 - 2*3   3 - 1*3   Hence max of 3^9 is allowed. IMO D.
<result>D</result>
If 21!/3^x is an integer, what is the greatest possible value of x?