What is the largest power of 5 which divides the product of an the first 100 positive integers: 1 X 2 X 3 X ... X 98 X 99 X 100?
A.5^2
B. 5^20
C. 5^24
D. 5^100
there are 20 multiples of 5 between 1 and 100.
Since 5^2=25, there are also 4 multiples of 5^2, so they have to be counted twice.