central limit theorem

1) Compute the standard deviation using sigma= sqrt( p (1-p) N ) = sqrt( .85 * .15 * 100) = 3.57

2) Determine how many standard deviations it is between your expected value (85) and the value of interest (90). 5/3.57 = 1.4

3) Find the probability on the cumulative distribution that corresponds to a z score of 1.4. That is the probability it will be less than 90, so take one minus that value.