# Thread: Help!! urgent need it on thursday (poisson)

1. ## Help!! urgent need it on thursday (poisson)

An old car is never garaged at. On the morning following a wet night, the probability that the car does not start is 1/3. On the morning following a dry night, this probability is 1/25. The starting of a car each morning is independent of its performance on previous morning

During a long summer drought there are 100 dry nights. Using a Poisson approximation, determine the probability that the car does not start on 5 or more of the 100 mornings.

2. Originally Posted by whleow
An old car is never garaged at. On the morning following a wet night, the probability that the car does not start is 1/3. On the morning following a dry night, this probability is 1/25. The starting of a car each morning is independent of its performance on previous morning

During a long summer drought there are 100 dry nights. Using a Poisson approximation, determine the probability that the car does not start on 5 or more of the 100 mornings.
The average is (100)(1/25) = 4.

So sub that into the Poisson formula and then calculate Pr(X > 4) = 1 - Pr(X < 5) ......