Andy and Jim are going to compete in the 100-meter dash against each other. Let A be the time it takes Andy to complete the race, and I be the time it takes Jim to complete the race. Based on previous results, they know
that pa = 11.5 seconds and o A = 1 second. They also know that pj = 10.5 seconds and oj = 0.5
seconds.
Assume that their times are independent. Let D be the difference between their times in a random 100-meter
dash (D = A - J).
Find the mean of D.