John Wiley & Sons TI-83 User Manual download pdf (Page 37)

Example: New Bank Accounts

Suppose that on the average two new accounts per day are opened at an Imperial Savings Branch

bank. Let’s find the probability that on a given day at least 7 new accounts are opened. The

complement of opening at least 7 new accounts is opening at most 6 new accounts, which has

probability poissoncdf(2, 6) = 0.9955. The probability of opening at least 7 new accounts is

1−0.9955 = 0.0045.

Geometric Probabilities

Your calculator can compute probabilities for a geometric random variable with probability of

success p using the geometpdf( command, located on the DISTR page. To find the probability of

the random variable taking the value x, type geometpdf(p, x).

Example: Car Ignition

Suppose that a car with a bad starter can be started 90% of the time by turning on the ignition.

What is the probability that it will take three tries to get the car started? Type geometpdf(0.9, 3);

the answer is 0.9%.

Cumulative Geometric Probabilities

As with the binomial and cumulative probability functions, there is a cumulative version

geometcdf( . It can be used to find the probability that a geometric random variable will take a

value of at most x by typing geometcdf(p, x).

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John Wiley & Sons TI-83 User Manual Page 37