In: Statistics and Probability
Suppose passengers arrive at the MTA train station following a Poisson distribution with parameter 9 and the unit of time 1 hour.
Next train will arrive either 1 hour from now or 2 hours from now, with a 50/50 probability.
i. E(train arrival time)
ii. E(number of people who will board the train)
iii. var(number of people who will board the train)
(i) The expectation of train arrival time is = 1 x 0.5 2 x 0.5 = 1.5 (ii Given that the train arrives at time t, the number of passengers arrived will follow Poisson distribution with parameter 9t. Hence E[Number of people arrived to board the train|The train has arrived at time t =9t E[Number of people arrived to board the train] -9 x E[The train has arrived at time t 9 x 1.5 = 13.5 (iii) Similarly Variance of number of people who have arrived given that the train arrives at time t is 9t. Hence Variance of number of people who have arrived is =9 x E[The train has arrived at time t]9 x Var[The train has arrived at time t =9 x 1.59 x [(1 - 1.5)2 x 0.5+ (2 1.5)2 x 0.5] = 13.5 9 x 0.25 = 15.75
(i) The expectation of train arrival time is =1 x 0.52 x 0.5 = 1.5 (ii Given that the train arrives at time t, the number of passengers arrived will follow Poisson distribution with parameter 9t. Hence E[Number of people arrived to board the train|The train has arrived at time t =9t .E[Number of people arrived to board the train] 9 x E[The train has arrived at time t] 9 x 1.5 = 13.5 (iii) Similarly Variance of number of people who have arrived given that the train arrives at time t is 9t. Hence Variance of number of people who have arrived is 9 x E[The train has arrived at time t] + 81 x Var[The train has arrived at time t =9 x 1.5 + 81 x [(1 - 1.5)2 x 0.5 (2 1.5)2 x 0.5 13.5 9 x 0.25 = 33.75