EXAMPLE 5.30

Number of dropped calls. Suppose that the number of dropped calls on your cell phone varies, with an average of 2.1 calls per day. If we assume that the Poisson setting is reasonable for this situation, we can model the daily count of dropped calls X using the Poisson distribution with What is the probability of having no more than two dropped calls tomorrow?

We can calculate either using software or the Poisson probability formula. Using the probability formula:

= 0.1225 + 0.2572 + 0.2700

= 0.6497

Using the R software, the probability is

These two answers differ slightly due to roundoff error in the hand calculation. There is roughly a 65% chance that you will have no more than two dropped calls tomorrow.