Thread: poisson with given

i know the poisson formula but how does a given condition affect it?

i.e. E(X)=3, find P(X=2|X>1).

i have X>1, as 1 - 4e^-3, and i can work out the normal P(X=2) but how does the given X>1 affect it? i dont know what to do

Originally Posted by mathcore

i know the poisson formula but how does a given condition affect it?

i.e. E(X)=3, find P(X=2|X>1).

i have X>1, as 1 - 4e^-3, and i can work out the normal P(X=2) but how does the given X>1 affect it? i dont know what to do

You're expected to understand conditional probability: .

Note that is equivalent to ....

so this will just be p(x=2)/p(x>1) then? just divide my own calculations

i get 0.28 is thAT RIGHT

Originally Posted by mathcore

so this will just be p(x=2)/p(x>1) then? just divide my own calculations Mr F says: Yes.

i get 0.28 is thAT RIGHT

If you have calculated each probability correctly and then done the arithmetic correctly then your answer will be correct.

yesh but thats what im asking if i did it correctly or not... is my result correct or not...?

Originally Posted by mathcore

i know the poisson formula but how does a given condition affect it?

i.e. E(X)=3, find P(X=2|X>1).

i have X>1, as 1 - 4e^-3, and i can work out the normal P(X=2) but how does the given X>1 affect it? i dont know what to do

Bayes' theorem can be used here:



where:



To two significant firures this gives which is your answer, but you should give more digits (even if they are zeros)

CB