A customer service department monitors how long their callers wait on hold before being helped. The time spent by the callers on hold follows a normal distribution similar to this: a histogram plots relative frequency versus time on hold in minutes. The x-axis goes from 0 to 8 and the y-axis goes from 0.00 to 0.40. The distribution is symmetrical between 0 and 8 with a mean frequency of 0.40 at approximately 4.5 minutes. Suppose that we took random samples of callers and calculated the sample mean time spent on hold for each sample of customers. We can assume that the callers in each sample are independent. What would be the shape of the sampling distribution of the sample mean?
a) Skewed to the right
b) Skewed to the left
c) Uniform
d) Normal