A-LevelMathematicsProbability and statistics9709/62 · Oct/Nov 2017 · Q13 Marks
Andy counts the number of emails, x, he receives each day and notes that, over a period of n days, Σ(x – 10) = 27 and the mean number of emails is 11.5. Find the value of n.
- Andy counts the number of emails, x, he receives each day and notes that, over a period of n days, Σ(x – 10) = 27 and the mean number of emails is 11.5. Find the value of n.[3]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.
- (M1 Expanding brackets and forming a three term equation involving 27 and at least one term in n, without x
- M1 10n or 11.5n seen in expression without x (1.5n = 27 implies M2)
- A1) n = 18
- OR: (M1 Dividing coded sum by n and forming a three term equation involving 11.5 and at least one term in n, without x
- M1 27/n seen in expression without x (1.5 = 27/n implies M2)
- A1) n = 18
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