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2.4.8 Normal distribution as a model (A-level only)

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Question 22

A deep-sea research submersible has a maximum payload capacity of 1200 kg1200\text{ kg}1200 kg.

The weights of Type A scientific crates are normally distributed with mean 110 kg110\text{ kg}110 kg and standard deviation 15 kg15\text{ kg}15 kg.

The weights of Type B scientific crates are normally distributed with mean 85 kg85\text{ kg}85 kg and standard deviation 10 kg10\text{ kg}10 kg.

Assume that the weights of individual crates are independent.

a.

Find the probability that when 6 Type A6\text{ Type A}6 Type A crates and 5 Type B5\text{ Type B}5 Type B crates are loaded onto the submersible, the total payload exceeds 1200 kg1200\text{ kg}1200 kg.

[4]
b.

The mission commander decides to set a limit on the total number of crates, ccc, that can be carried on a single dive. Find the largest integer value of ccc such that the probability of the total payload exceeding 1200 kg1200\text{ kg}1200 kg is less than 2%2\%2%, regardless of the combination of crate types used.

[4]

2.4.8 Normal distribution as a model (A-level only) Questions

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