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

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Question 21

A service elevator has a maximum load capacity of 900 kg900\text{ kg}900 kg.

The weights of adult males are normally distributed with mean 82 kg82\text{ kg}82 kg and standard deviation 12 kg12\text{ kg}12 kg.

The weights of adult females are normally distributed with mean 68 kg68\text{ kg}68 kg and standard deviation 8 kg8\text{ kg}8 kg.

Assume that the weights of individual people are independent.

a.

Find the probability that when 7 males7\text{ males}7 males and 4 females4\text{ females}4 females are in the elevator, the total load exceeds 900 kg900\text{ kg}900 kg.

[4]
b.

The elevator displays a sign stating: "Maximum occupancy is ccc persons."

Find the largest integer value of ccc such that the probability of the total load exceeding 900 kg900\text{ kg}900 kg is less than 1%1\%1%, regardless of the gender distribution of the occupants.

[5]

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

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