Exam-Style Problems

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Nov 2007 p6 q7
2952

Box A contains 5 red paper clips and 1 white paper clip. Box B contains 7 red paper clips and 2 white paper clips. One paper clip is taken at random from box A and transferred to box B. One paper clip is then taken at random from box B.

The random variable X denotes the number of times that a red paper clip is taken. Draw up a table to show the probability distribution of X.

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June 2022 p52 q2
2953

A fair 6-sided die has the numbers 1, 2, 2, 3, 3, 3 on its faces. The die is rolled twice. The random variable X denotes the sum of the two numbers obtained.

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

(b) Find E(X) and Var(X).

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June 2007 p6 q7
2954

A vegetable basket contains 12 peppers, of which 3 are red, 4 are green and 5 are yellow. Three peppers are taken, at random and without replacement, from the basket.

The number of green peppers taken is denoted by the discrete random variable X. Draw up a probability distribution table for X.

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Nov 2005 p6 q6
2955

In a competition, people pay $1 to throw a ball at a target. If they hit the target on the first throw they receive $5. If they hit it on the second or third throw they receive $3, and if they hit it on the fourth or fifth throw they receive $1. People stop throwing after the first hit, or after 5 throws if no hit is made. Mario has a constant probability of \(\frac{1}{5}\) of hitting the target on any throw, independently of the results of other throws.

  1. Mario misses with his first and second throws and hits the target with his third throw. State how much profit he has made.
  2. Show that the probability that Mario’s profit is $0 is 0.184, correct to 3 significant figures.
  3. Draw up a probability distribution table for Mario’s profit.
  4. Calculate his expected profit.
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June 2005 p6 q3
2956

A fair dice has four faces. One face is coloured pink, one is coloured orange, one is coloured green and one is coloured black. Five such dice are thrown and the number that fall on a green face are counted. The random variable \(X\) is the number of dice that fall on a green face.

(i) Show that the probability of 4 dice landing on a green face is 0.0146, correct to 4 decimal places.

(ii) Draw up a table for the probability distribution of \(X\), giving your answers correct to 4 decimal places.

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