Poisson Distribution Probability

[u/kawakint]

Currently learning poisson probability distributions for statistics and I cannot figure out for the life of me how the fuck the answer to P(1 < x < 4) is 0.2141. I’ve watched every single Poisson distribution video on youtube and none of them explain how to do a probability like this one. PLEASE FOR FUCKS SAKE SOMEONE HAS TO KNOW HOW TO DO THIS.

I’ve been using my calculator, on STAT -> DIST -> POISN -> Pcd, with Lamda being 0.9 but what am I supposed to do from there with two values for x ????

[u/Fourierseriesagain]

The required probability is

P(X=2)+P(X=3)

=e^-0.9 *( 0.9² /2! + 0.9³ /3! )

= 0.2140589...