Each week Border's buys and sellsSporting Weekly. They buy each copy wholesale for 80¢ and sell it retail for $2.00. At the end of the week they can sell any unsold copies for a salvage value of 40¢. Suppose the probability,Pr{d}, that people want to buydcopies in any given week is given by

Pr{d} = { (d+1)/110 for d=0,1,2,....9

(20-d)/110 for d=10,11,12,...,19

How many copies should Border's buy wholesale each week in order to maximize the expected profit?

The formula 1 + 2 + … +n= (n+1)/2 might be useful to find the cumulative distribution function for the demand.