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A-LevelMathematicsProbability and statistics9709/61 · May/June 2021 · Q32 Marks

The graph of the probability density function of a random variable X is symmetrical about the line x = 4.

  1. Given that P(X < 5) = 20/27, find P(3 < X < 5).[2]

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

  1. [M1] `1 - 20/27 - 1/2` or `20/27 - 1/2` or `1 - (20/27 - 1/2)`. For either expression seen.
  2. [A1] `13/27` OE. Accept 0.481 or 0.482.

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About this question

Topic
Probability and statistics, A-Level Mathematics (syllabus 9709). Structured question, 2 marks.
Source
A-Level Mathematics, May/June 2021 Paper 6 Variant 1, question 3.

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