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A-LevelMathematicsProbability and statistics9709/62 · Feb/Mar 2018 · Q56 Marks

A summary of n values of x gave the following information: Σ(x – 20) = 136, Σ(x – 20)² = 2888. The mean of the n values of x is 24.25.

  1. (i)Find the value of n.[2]
  2. (ii)Find Σx².[4]

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2018). The mark or mark type is shown in brackets.

  1. [M1] Unsimplified correct equation
  2. [A1]
  3. [M1] unsimplified expression for variance
  4. [A1] accept answers 72.2 SOI
  5. [M1] Equate two expressions for variance and solve
  6. [A1]

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About this question

Topic
Probability and statistics, A-Level Mathematics (syllabus 9709). Structured question, 6 marks.
Source
A-Level Mathematics, Feb/Mar 2018 Paper 6 Variant 2, question 5.

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