# Poisson Distribution using probabilities

#### Ipsita Bhattacharya

##### New Member
If X follows a poisson distribution where P(X=1)=0.4,P(X=2)=0.6, what is the value of P(X=0)? How will I solve this question?

#### Englund

##### TS Contributor
I think those probabilities are impossible if X is modeled as a poisson process. But, assuming they are possible: What is the probability of X being non-negative?

#### Ipsita Bhattacharya

##### New Member
Actually the answer is positive. That means the question is somehow incorrect?

#### Englund

##### TS Contributor
The probability of a non-negative result is 1. What should P(X=0) be if P(X=1) + P(X=2) = 1?

#### amilsan

##### New Member
but exp(something) = 0 ? thats not possible ln(0), plus in poisson P(X=0) is the highest value
perhaps with the cumulative P(x=1)=0.4 P(x=2)=0.67 with d=2 but i didnt find the answer to that neither
if that 1 or 2 happen conditionally after 100 tries, so in 100 you will have 1 or 2 (if the event happens) or 0 (99% of time), perhaps that could be a poisson aprox