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 ?
"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 ."
divide(const_2, 5)