Mathematics 9709 · AS & A Level · The Poisson distribution

The Poisson distribution — practice question

On average, a website owner sees $0.3$ hits each minute on his website. He thinks that the hits per minute are described by a Poisson distribution.
(a(i))[3]

Assuming the owner is right, determine the probability that there are at least $4$ hits in a $10$-minute interval.

(a(ii))[4]

Use an appropriate approximating distribution to determine the probability that there are fewer than $40$ hits in a $3$-hour interval.

(a)

Assume the owner is correct.

(b)

A friend also accepts that the website gets, on average, $0.3$ hits per minute. Even so, she observes that the number of hits in the day-time ($9.00\ \text{am}$ to $9.00\ \text{pm}$) is usually about twice the number of hits in the night-time ($9.00\ \text{pm}$ to $9.00\ \text{am}$).

(b(i))[1]

Explain why this observation contradicts the owner’s belief that the number of hits per minute follows a Poisson distribution.

(b(ii))[2]

State separate Poisson distributions that could reasonably model the number of hits during the day-time and during the night-time.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: Mean correctly given as $\lambda=3$.

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