Exam-Style Problems

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Feb/Mar 2022 p52 q2
2990

In a certain country, the probability of more than 10 cm of rain on any particular day is 0.18, independently of the weather on any other day.

(a) Find the probability that in any randomly chosen 7-day period, more than 2 days have more than 10 cm of rain.

(b) For 3 randomly chosen 7-day periods, find the probability that exactly two of these periods have at least one day with more than 10 cm of rain.

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Nov 2021 p53 q6
2991

In a game, Jim throws three darts at a board. This is called a ‘turn’. The centre of the board is called the bull’s-eye.

The random variable \(X\) is the number of darts in a turn that hit the bull’s-eye. The probability distribution of \(X\) is given in the following table.

\(x\)0123
\(P(X = x)\)0.6pq0.05

It is given that \(E(X) = 0.55\).

  1. (a) Find the values of \(p\) and \(q\).
  2. Jim is practising for a competition and he repeatedly throws three darts at the board.
  3. (c) Find the probability that \(X = 1\) in at least 3 of 12 randomly chosen turns.
  4. (d) Find the probability that Jim first succeeds in hitting the bull’s-eye with all three darts on his 9th turn.
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Nov 2021 p52 q5
2992

In a certain region, the probability that any given day in October is wet is 0.16, independently of other days.

Find the probability that, in a 10-day period in October, fewer than 3 days will be wet.

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June 2021 p53 q7
2993

In the whole of Arka there are a large number of households. A survey showed that 35% of households in Arka have no broadband service.

(i) 10 households in Arka are chosen at random.

Find the probability that fewer than 3 of these households have no broadband service. [3]

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June 2021 p52 q5
2994

Every day Richard takes a flight between Astan and Bejin. On any day, the probability that the flight arrives early is 0.15, the probability that it arrives on time is 0.55 and the probability that it arrives late is 0.3.

(a) Find the probability that on each of 3 randomly chosen days, Richard's flight does not arrive late.

(b) Find the probability that for 9 randomly chosen days, Richard's flight arrives early at least 3 times.

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