If an integer n is to be selected at random from 1 to 99, inclusive, what is probability n(n+1) will be divisible by 3?  Choose the correct choice from the following:
A) 1/4  B) 1/3  C) 1/2  D) 2/3  E) 3/4
For n(n+1) to be a multiple of 3, either n or n+1 has to be a multiple of 3.   Thus n must be of the form 3k or 3k-1, but not 3k+1.   The probability is 2/3.   The answer is 2/3.
<result>D</result>
If an integer n is to be selected at random from 1 to 99, inclusive, what is probability n(n+1) will be divisible by 3?