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.

The table is:0 1 2 3 

x1 0 0.08 0.06 0.04 0.00 

1 0.05 0.18 0.05 0.03 

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 

Expected difference =
+(0.08*(0-0)) +(0.06*(0-1)) +(0.04*(0-2)) +(0.00*(0-3)) +(0.05*(1-0)) +(0.18*(1-1)) +(0.05*(1-2)) +(0.03*(1-3)) +(0.05*(2-0)) +(0.04*(2-1)) +(0.10*(2-2)) +(0.06*(2-3)) +(0.00*(3-0)) +(0.03*(3-1)) +(0.04*(3-2)) +(0.07*(3-3)) +(0.00*(4-0)) +(0.01*(4-1)) +(0.05*(4-2)) +(0.06*(4-3))
= 0.17