Exam-Style Problems

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June 2023 p51 q7
3040

A children's wildlife magazine is published every Monday. For the next 12 weeks it will include a model animal as a free gift. There are five different models: tiger, leopard, rhinoceros, elephant, and buffalo, each with the same probability of being included in the magazine.

Sahim buys one copy of the magazine every Monday.

(b) Find the probability that Sahim will get more than two leopards in the 12 magazines.

(c) Find the probability that after 5 weeks Sahim has exactly one of each animal.

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Nov 2013 p62 q5
3041

On trains in the morning rush hour, each person is either a student with probability 0.36, or an office worker with probability 0.22, or a shop assistant with probability 0.29 or none of these.

8 people on a morning rush hour train are chosen at random. Find the probability that between 4 and 6 inclusive are office workers.

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Nov 2012 p61 q5
3042

A company set up a display consisting of 20 fireworks. For each firework, the probability that it fails to work is 0.05, independently of other fireworks.

(i) Find the probability that more than 1 firework fails to work.

The 20 fireworks cost the company $24 each. 450 people pay the company $10 each to watch the display. If more than 1 firework fails to work they get their money back.

(ii) Calculate the expected profit for the company.

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June 2012 p63 q5
3043

Suzanne has 20 pairs of shoes, some of which have designer labels. She has 6 pairs of high-heeled shoes, of which 2 pairs have designer labels. She has 4 pairs of low-heeled shoes, of which 1 pair has designer labels. The rest of her shoes are pairs of sports shoes. Suzanne has 8 pairs of shoes with designer labels in total.

Suzanne chooses 1 pair of shoes at random each day.

Find the probability that Suzanne wears a pair of shoes with designer labels on at most 4 days out of the next 7 days.

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June 2012 p61 q4
3044

In a certain mountainous region in winter, the probability of more than 20 cm of snow falling on any particular day is 0.21.

  1. Find the probability that, in any 7-day period in winter, fewer than 5 days have more than 20 cm of snow falling.
  2. For 4 randomly chosen 7-day periods in winter, find the probability that exactly 3 of these periods will have at least 1 day with more than 20 cm of snow falling.
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