Question

A certain market has both an express checkout line and a super-express checkout line. Let X₁ denote the number of customers in line at the express checkout at a particular time of day, and let X₂ denote the number of customers in line at the superexpress checkout at the same time. Suppose the joint pmf of X₁ and X₂ is as given in the accompanying table.

		x2
		0	1	2	3
x1	0	0.08	0.06	0.04	0.00
	1	0.07	0.13	0.05	0.06
	2	0.05	0.04	0.10	0.06
	3	0.00	0.03	0.04	0.07
	4	0.00	0.01	0.05	0.06

The difference between the number of customers in line at the express checkout and the number in line at the superexpress checkout is X₁ − X₂. Calculate the expected difference.

Answer 1