Each day hundreds of deliveries are scheduled. The manager decides to monitor the time

deviations by taking a random sample of 100 deliveries and calculating the average deviation

defined by D bar = 1/100 * Sigma 100/i=1 * D sub i, for each day. Assume that historical data such as that displayed in part (1) suggests that the distribution of deviations Di have a mean of 27.9 and standard deviation

of 31. Find the probability that the sample mean is greater than 30.

(i.e. Find P[ D bar > 30] for a sample of size n=100).

I'm having a hard time understanding how to incorporate D bar > 30.