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2.4.4 Mean and variance of the binomial (A-level only)

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Question 54

A shipment contains 30 custom-built sensor units. Each unit has a probability of 0.2 of being classified as 'High-Precision'. Let the random variable KKK represent the number of 'High-Precision' units in the shipment.

a.

State a suitable distribution to model KKK.

[1]
b.

A distributor makes a profit of £5 on each 'High-Precision' unit but loses £2 on every unit that is not 'High-Precision' due to recalibration costs. Let VVV be the random variable representing the distributor's total profit/loss from the shipment.

Show that V=7K−60V = 7K - 60V=7K−60.

[2]
c.

Find E(V)E(V)E(V) and Var(V)Var(V)Var(V).

[4]
d.

Calculate P(V≥10)P(V \ge 10)P(V≥10).

[2]
e.

A larger production facility produces 200 sensor units. The facility manager claims that for this specific batch, the probability of a unit being 'High-Precision' is 0.15.

Using a suitable approximation, estimate the probability that at least 40 units in this batch are 'High-Precision'.

[5]

2.4.4 Mean and variance of the binomial (A-level only) Questions

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