explaination please Rework problem 25 from section 35 of you

explaination please

Rework problem 25 from section 3.5 of your text involving a car saleswoman. Assume that showing a car is a Bernoulli trial, and each time she shows a car, there is a probability of 0.15 that the customer will buy the car. The saleswoman has a goal of selling at least one car a week. How many cars must she show so that the probability of her reaching her goal is at least 0.99?

Solution

let the # of cars needed to be showen = n
P[sell at least 1 car] = 1 - P[sell no car] = 1 - 0.85^n
1 - 0.85^n >= 0.99
0.85^n < = 0.01
n*ln 0.85 < = ln 0.02
n > = ln 0.02/ln 0.85 > = 28.33 => 29
[ inequality sign reversed as divided by ln 0.85, a negative # ]

ans: 29 cars