It is a Poi Process
This is a Poisson process based question.
Here you consider number of events in given time interval (= lambda L * t), instead of events per unit time (lambda L).
Using Poi(lambda L t)
Event 1 - You have 1 visitor in 30 mins ( 1/2 hrs) = prob = ( (Lt)^1 * e ^ -Lt ) / 1!
&
Event 2 - You have 4 visitors in 2 hrs = prob = ( (Lt)^4 * e^ -Lt) / 4!
Poi Dist is memoryless, so 1st visitor in 1/2 hr does not effect prob of 4 more visitors in next 2 hrs.
Also 2 events are indipendent. So we can multiply the probs.
So::: ( (Lt)^1 * e ^ -Lt ) / 1! * ( (Lt)^4 * e^ -Lt) / 4! = Answer
Last edited by a moderator: May 15, 2009