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2.3.3 Conditional probability (A-level only)

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Question 1

The time taken to fully charge the high-capacity battery of a specialized cargo drone follows a normal distribution with a mean of 140 minutes140\text{ minutes}140 minutes and a standard deviation of 12 minutes12\text{ minutes}12 minutes.

a.

Determine the probability that a randomly selected battery charge takes longer than 155 minutes155\text{ minutes}155 minutes.

[2]
b.

Any battery charge that takes longer than 155 minutes155\text{ minutes}155 minutes is classified as an "extended duration" charge.

A drone's battery charge is monitored at random. Given that it is classified as an extended duration charge,

calculate the probability that the charge takes longer than 165 minutes165\text{ minutes}165 minutes.

[4]
c.

Among the extended duration charges, exactly 15%15\%15% last longer than m minutesm\text{ minutes}m minutes.

Find the value of mmm.

[4]

2.3.3 Conditional probability (A-level only) Questions

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