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?
Pick one:
A) 1 / 5	B) 1 / 3	C) 1 / 2	D) 2 / 3	E) 2 / 5

Rationale: "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 5 k or 5 k - 1 . the probability is 2 / 5 . the answer is e ."
Answer: E