# Knowledge Base

## Solution 29450: How to Calculate the Poisson Pdf and Poisson Cdf on the TI-Nspire™ Family Line of Products.

### How is the Poissonpdf and Poissoncdf probability calculated on the TI-Nspire Family line of products?

The Poisson Pdf computes a probability for a discrete Poisson distribution with a specified mean lambda. The proper syntax is poisspdf(lambda, x). The parameters in lambda must all be positive. X can be any nonnegative integer. The density function is zero unless x is an integer.

Poisson Cdf is used to calculate Poisson distribution cumulative probability with specified mean lambda. The syntax is poissCdf(lambda, lower bound, upper bound).

Poisson pdf example:

A computer hard disk manufacturer has observed that flaws occur randomly in the manufacturing process at the average rate of three flaws in a 10 GB hard disk and has found this rate to be acceptable. What is the probability that a disk will be manufactured with no defects?

In this problem:

lambda = 2
x = 0

1) Press [home].
2) Press [A] or choose "Add Calculator". 3) Press [menu]   [H].  4) Press  [tab]  [enter] [enter].  Poisson cdf example:

Consider point on a city street where an average of 5 cars pass by each minute. What is the probability that in a given minute, no more than 3 cars will drive by? The event is a car passing by, which happens at an average rate of 5 occurences per time interval (a minute). Each occurrence is independent of the time since the last occurrence (assuming this is true, though traffic might imply a correlation here). We're interested in the probability that the event occurs at most 3 times in the time interval.

1) Press [home].
2) Press [A] or choose "Add Calculator".
3) Press [menu]   [I].  4) Press  [tab]  [tab]  [enter] [enter].  This will give about .265 when computed, so there's a .265 probability that in a given minute, no more than 3 cars will drive by.