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

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Question 29

The independent random variables CCC and DDD represent the volumes, in millilitres, of coffee dispensed by 'Classic' and 'Deluxe' pods respectively, where

C∼N(45,1.22)andD∼N(60,1.62) C \sim \mathrm{N}(45, 1.2^2) \quad \text{and} \quad D \sim \mathrm{N}(60, 1.6^2) C∼N(45,1.22)andD∼N(60,1.62)

The random variables C1,C2C_1, C_2C1​,C2​ are independent and each has the same distribution as CCC. The random variables D1,D2,D3D_1, D_2, D_3D1​,D2​,D3​ are independent and each has the same distribution as DDD.

Given that the random variable MMM is defined as

M=C1+C2+D1+D2+D35 M = \frac{C_1 + C_2 + D_1 + D_2 + D_3}{5} M=5C1​+C2​+D1​+D2​+D3​​
a.

find P(M<52.5)P(M < 52.5)P(M<52.5).

[4]
b.

The random variable VVV represents the volume dispensed by a 'Value' pod, such that V∼N(μ,3.52)V \sim \mathrm{N}(\mu, 3.5^2)V∼N(μ,3.52).

Given that P(V−C<8)=0.12P(V - C < 8) = 0.12P(V−C<8)=0.12 and that VVV and CCC are independent,

find the value of μ\muμ, giving your answer to 3 significant figures.

[4]

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

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