Which one of the following numbers is the greatest positive integer x such that 3^x is a factor of 81^5?	Choose one
A) 5 B) 8 C) 10 D) 15 E) 20
81 = 3*3*3*3= 3^4   81^5 =(3^4)^5   =3^20   we have to find the greatest positive integer value for x   when x=20, it divides exactly once and that is the least positive integer value of the quotient   therefore, the correct option is 20
<result>E</result>
Which one of the following numbers is the greatest positive integer x such that 3^x is a factor of 81^5?