Exam-Style Problems

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June 2020 p51 q3
2897

A company produces small boxes of sweets that contain 5 jellies and 3 chocolates. Jemeel chooses 3 sweets at random from a box.

Draw up the probability distribution table for the number of jellies that Jemeel chooses.

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June 2023 p53 q3
2898

The random variable X takes the values 1, 2, 3, 4. It is given that \(P(X = x) = kx(x + a)\), where \(k\) and \(a\) are constants.

  1. Given that \(P(X = 4) = 3P(X = 2)\), find the value of \(a\) and the value of \(k\).
  2. Draw up the probability distribution table for X, giving the probabilities as numerical fractions.
  3. Given that \(E(X) = 3.2\), find \(\text{Var}(X)\).
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Feb/Mar 2020 p52 q2
2899

An ordinary fair die is thrown 3 times. The random variable X is the number of times that a 1 or a 6 is obtained.

(b) Draw up the probability distribution table for X.

(c) Find E(X).

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Nov 2019 p63 q6
2900

A box contains 3 red balls and 5 white balls. One ball is chosen at random from the box and is not returned to the box. A second ball is now chosen at random from the box.

  1. Find the probability that both balls chosen are red.
  2. Show that the probability that the balls chosen are of different colours is \(\frac{15}{28}\).
  3. Given that the second ball chosen is red, find the probability that the first ball chosen is red.

The random variable \(X\) denotes the number of red balls chosen.

  1. Draw up the probability distribution table for \(X\).
  2. Find \(\text{Var}(X)\).
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Nov 2019 p62 q5
2901

A fair red spinner has four sides, numbered 1, 2, 3, 3. A fair blue spinner has three sides, numbered -1, 0, 2. When a spinner is spun, the score is the number on the side on which it lands. The spinners are spun at the same time. The random variable X denotes the score on the red spinner minus the score on the blue spinner.

(i) Draw up the probability distribution table for X.

(ii) Find \(\text{Var}(X)\).

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