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2.3 Probability

2.3 Probability

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Question 69

The masses of a specific breed of adult dog are normally distributed with a mean of 24 kg24\text{ kg}24 kg and a standard deviation of 5 kg5\text{ kg}5 kg.

a.

Find the probability that a randomly selected dog from this breed has a mass greater than 31.5 kg31.5\text{ kg}31.5 kg.

[3]
b.

Any dog of this breed with a mass greater than 31.5 kg31.5\text{ kg}31.5 kg is classified as "heavy".

A dog of this breed is chosen at random. Given that it is classified as heavy,

find the probability that it has a mass greater than 36 kg36\text{ kg}36 kg.

[4]
c.

Among the heavy dogs, exactly 25%25\%25% have a mass greater than m kgm\text{ kg}m kg.

Find the value of mmm.

[4]
Markscheme

2.3 Probability Questions

  1. A Level
  2. /Maths
  3. /2.3 Probability

200 exam-style questions on OCR A Level Maths 2.3 Probability, covering 2.3.1 Mutually exclusive and independent events, 2.3.2 Diagrams to assist probability calculations, 2.3.3 Conditional probability (A-level only), 2.3.4 Conditional probability from first principles (A-level only), and 2.3.5 Modelling with probability. Each one has a worked solution and a mark scheme showing where the marks go.

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