The average number of phone inquiries per day at the poison control center is 4. Find the probability it will receive 5 calls on a given day. Use the Poisson approximation.

Okay, so I think that n = 4 and x = 5, but I have no idea how I would get p from this word problem... If you're good at statistics, please help meee~

Question

The average number of phone inquiries per day at the poison control center is 4. Find the probability it will receive 5 calls on a given day. Use the Poisson approximation. 

Okay, so I think that n = 4 and x = 5, but I have no idea how I would get p from this word problem... If you're good at statistics, please help meee~

perl · Answer

$$ \Large {

P(X=k) = e^{-\lambda} ~\frac{\lambda ^k}{k!}~,~ k=0,1,2,3...


} $$