TI-84 Plus CE field manual for IB Math
Poisson distribution probabilities
Use the Poisson cdf routine to find bounded probabilities P(a≤X≤b).
If X∼Po(4), find P(2≤X≤6).
Open the distribution menu with and scroll down to E: poissoncdf(. This routine gives P(X≤x), so a two-sided range is the difference of two calls.
Fill in the wizard for the upper bound: μ=4 and x value: 6.
Highlight Paste and press . The wizard closes and poissoncdf(4,6) pastes onto the home screen. Now subtract the lower piece: press (the subtraction key), reopen poissoncdf(, and paste it again with μ=4, x value: 1. Subtracting at 1 (not 2) keeps X=2 inside the range.
With both calls on the home screen, press to evaluate: P(2≤X≤6)≈0.798.
Your turn
Work each one on your calculator, then check the answer.
- 1
If X∼Po(5.5), find P(3≤X≤7).
- 2
If X∼Po(3), find P(2≤X≤5).
- 3
If X∼Po(7), find P(5≤X≤9).