If an integer n is to be selected at random from 1 to 100, inclusive, what is probability n(n+1) will be divisible by 5? Select the correct option:
A) 1/5
B) 1/3
C) 1/2
D) 2/3
E) 2/5
For n(n+1) to be a multiple of 5, either n or n+1 has to be a multiple of 5.   Thus n must be of the form 5k or 5k-1.   The probability is 2/5.   The answer is 2/5.
<result>E</result>
If an integer n is to be selected at random from 1 to 100, inclusive, what is probability n(n+1) will be divisible by 5?