When an opinion poll selects cell phone numbers at random to dial, the cell phone exchange is first selected, and then random digits are added to form a complete telephone number (see Example 8.5). When using this procedure to generate random cell phone numbers, approximately 55% of the cell numbers generated correspond to working numbers. You watch a pollster dial cell numbers that have been selected in this manner. X is the number of calls dialed before the third working cell number is reached.