A telemarketer makes successive independent calls with succe

A telemarketer makes successive independent calls with success (sale) probability p=0.1. The calls cost $0.50 each. What is the expected cost of obtaining the first sale?

Solution

Number of calls untill success is geomteric random variable with p = 0.1, Expected number of calls = 1/p = 10

Expected cost for first sale = 0.5*10 = $5