Exam-Style Problems

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June 2017 p62 q7
2607

During the school holidays, each day Khalid either rides on his bicycle with probability 0.6, or on his skateboard with probability 0.4. Khalid does not ride on both on the same day. If he rides on his bicycle then the probability that he hurts himself is 0.05. If he rides on his skateboard the probability that he hurts himself is 0.75.

(i) Find the probability that Khalid hurts himself on any particular day.

(ii) Given that Khalid hurts himself on a particular day, find the probability that he is riding on his skateboard.

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June 2017 p61 q3
2608

Redbury United soccer team play a match every week. Each match can be won, drawn or lost. At the beginning of the soccer season the probability that Redbury United win their first match is \(\frac{3}{5}\), with equal probabilities of losing or drawing. If they win the first match, the probability that they win the second match is \(\frac{7}{10}\) and the probability that they lose the second match is \(\frac{1}{10}\). If they draw the first match they are equally likely to win, draw or lose the second match. If they lose the first match, the probability that they win the second match is \(\frac{3}{10}\) and the probability that they draw the second match is \(\frac{1}{20}\).

  1. Draw a fully labelled tree diagram to represent the first two matches played by Redbury United in the soccer season.
  2. Given that Redbury United win the second match, find the probability that they lose the first match.
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Nov 2016 p62 q1
2609

When Anya goes to school, the probability that she walks is 0.3 and the probability that she cycles is 0.65; if she does not walk or cycle she takes the bus. When Anya walks the probability that she is late is 0.15. When she cycles the probability that she is late is 0.1 and when she takes the bus the probability that she is late is 0.6. Given that Anya is late, find the probability that she cycles.

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Nov 2016 p61 q6
2610

Deeti has 3 red pens and 1 blue pen in her left pocket and 3 red pens and 1 blue pen in her right pocket. 'Operation T' consists of Deeti taking one pen at random from her left pocket and placing it in her right pocket, then taking one pen at random from her right pocket and placing it in her left pocket.

(i) Find the probability that, when Deeti carries out operation T, she takes a blue pen from her left pocket and then a blue pen from her right pocket.

The random variable X is the number of blue pens in Deeti's left pocket after carrying out operation T.

\((ii) Find P(X = 1).\)

(iii) Given that the pen taken from Deeti's right pocket is blue, find the probability that the pen taken from Deeti's left pocket is blue.

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June 2016 p62 q1
2611

Ayman’s breakfast drink is tea, coffee or hot chocolate with probabilities 0.65, 0.28, 0.07 respectively. When he drinks tea, the probability that he has milk in it is 0.8. When he drinks coffee, the probability that he has milk in it is 0.5. When he drinks hot chocolate he always has milk in it.

(i) Draw a fully labelled tree diagram to represent this information.

(ii) Find the probability that Ayman’s breakfast drink is coffee, given that his drink has milk in it.

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