what is the probability in a given month

Question

Assume that cases of mumps are random and independent and the number X of monthly mumps cases in Michigan has approximately the Poisson distribution with  = 0.2.  What is the probability that in a given month there is no more than 1 case?

Answer 1

No more than one case is the same as P(x≤1). So the chance of success is 0.2 and the random variable is 1.

 

So to find the chance P(x≤1), add P(x=0) and P(x=1)