How to approach this problem?
If p is the product of the integers from 1 to 30, inclusive, what is the greatest integer k for which 3^k is a factor of p ?
(A) 10
(B) 12
(C) 14
(D) 16
(E) 18
Hi Kukrejaria,
Here given P is 30! (30 factorial).
Question is :
If 3^k is factor of 30!, then what is the maximum value of k ?
All we need to do is count the number of 3’s in the 30!.
So,
3 , 6, 9, 12, 15,18, 21, 24,27 and 30.
Above is the list, where we find the 3’s in the 30 factorial.
But in the above list,
9, 18 – counts for two three’s because you have 3^2 in it.
and 27 – counts for three 3’s in it, because 3^3 = 27.
So there are totally, 14 three’s in it.
So the answer is C.
Shortcut to find the same would be,
Find 3’s, 3^2’s and 3^3’s like I have done below,
(30/ 3) + (30/ 3^2) + (30 / 3^3)
= 10 + 3 + 1
= 14.
Hope this helps.