Exam-Style Problems

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Nov 2023 p53 q1
2887

Becky sometimes works in an office and sometimes works at home. The random variable \(X\) denotes the number of days that she works at home in any given week. It is given that

\(P(X = x) = kx(x+1)\),

where \(k\) is a constant and \(x = 1, 2, 3\) or \(4\) only.

(a) Draw up the probability distribution table for \(X\), giving the probabilities as numerical fractions.

(b) Find \(E(X)\) and \(\text{Var}(X)\).

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Nov 2021 p51 q4
2888

A fair spinner has edges numbered 0, 1, 2, 2. Another fair spinner has edges numbered -1, 0, 1. Each spinner is spun. The number on the edge on which a spinner comes to rest is noted. The random variable X is the sum of the numbers for the two spinners.

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

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

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June 2021 p52 q4
2889

A fair spinner has sides numbered 1, 2, 2. Another fair spinner has sides numbered -2, 0, 1. Each spinner is spun. The number on the side on which a spinner comes to rest is noted. The random variable X is the sum of the numbers for the two spinners.

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

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

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June 2021 p51 q7
2890

Sharma knows that she has 3 tins of carrots, 2 tins of peas and 2 tins of sweetcorn in her cupboard. All the tins are the same shape and size, but the labels have all been removed, so Sharma does not know what each tin contains.

Sharma wants carrots for her meal, and she starts opening the tins one at a time, chosen randomly, until she opens a tin of carrots. The random variable \(X\) is the number of tins that she needs to open.

(a) Show that \(P(X = 3) = \frac{6}{35}\).

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

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

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Feb/Mar 2021 p52 q4
2891

The random variable X takes the values 1, 2, 3, 4 only. The probability that X takes the value x is k(5 โˆ’ x), where k is a constant.

(a) Draw up the probability distribution table for X, in terms of k.

\((b) Show that Var(X) = 1.05.\)

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