Calculate a normal probability and an inverse normal quantile.

Calculate a normal probability and an inverse normal quantile.

6 marks
ProbabilityQuestionBank.pdf

A random variable \(X\) is distributed normally with mean \(450\) and standard deviation \(20\).

  1. Find \(P(X ≤ 475)\).[2]
  2. Given that \(P(X > a) = 0.27\), find \(a\).

    [4]

Solution:

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Answer:Since \(P(X>a)=0.27\), \(P(X\le a)=0.73\) and \(z=0.6128\). Thus \(a=450+20(0.6128)=462\) approximately.

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