Mathematics 9709 · AS & A Level · The Poisson distribution

The Poisson distribution — practice question

A website owner notices that, on average, the site gets $0.3$ hits per minute. He thinks the number of hits per minute is modelled by a Poisson distribution.
(a(i))[3]

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

(a(ii))[4]

Use a suitable approximating distribution to determine the chance of fewer than $40$ hits in a $3$-hour interval.

(b(i))[1]

A friend accepts that the website averages $0.3$ hits per minute. However, she observes that the number of hits in the daytime ($9.00\,\text{am}$ to $9.00\,\text{pm}$) is usually about double the number in the night-time ($9.00\,\text{pm}$ to $9.00\,\text{am}$). Explain why this conflicts with the owner’s belief that the number of hits per minute follows a Poisson distribution.

(b(ii))[2]

State separate Poisson distributions that could be appropriate models for the number of hits in the daytime and in 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: Poisson mean $\lambda=3$ identified.

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