A-LevelMathematicsProbability and statistics9709/61 · May/June 2017 · Q14 Marks
Kadijat noted the weights, x grams, of 30 chocolate buns. Her results are summarised by Σ(x − k) = 315, Σ(x − k)² = 4022, where k is a constant. The mean weight of the buns is 50.5 grams.
- (i)Find the value of k.[2]
- (ii)Find the standard deviation of x.[2]
Mark scheme
Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.
- [M1] Dividing 315 by ±30 and + or – from 50.5 need both and no more
- [A1] Correct answer from correct working
- [M1] Mult by 50.5 by 30 and + or – 315 and dividing by ±30 need all these
- [A1] Correct answer from correct working. 1200 gets M0
- [M1] Subst in correct coded variance formula
- [A1]
- [M1] Expanding with ± 40Ex and ± 30(40)² seen
- [A1]
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