Mathematics 9709 · AS & A Level · Discrete random variables
Discrete random variables — practice question
A wildlife magazine for children is issued every Monday. During the next 12 weeks, each edition will come with a model animal as a free gift. The five possible models are tiger, leopard, rhinoceros, elephant and buffalo, and each has the same chance of being placed in the magazine. Sahim purchases one copy of the magazine every Monday.
(a)[2]
Find the probability that the first time the free gift is an elephant is before the 6th Monday.
(b)[3]
Find the probability that Sahim gets more than two leopards in the 12 magazines.
(c)[3]
Find the probability that after 5 weeks Sahim has exactly one of each animal.
Worked solution & mark scheme
This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Correct use of the complement $1-0.8^5$ or an equivalent sum of probabilities.” …