A-LevelMathematicsProbability and statistics9709/51 · May/June 2024 · Q14 Marks
A summary of 20 values of x gives Σ(x−30) = 439, Σ(x−30)² = 12405. A summary of another 25 values of x gives Σ(x−30) = 470, Σ(x−30)² = 11346.
- (a)Find the mean of all 45 values of x.[2]
- (b)Find the standard deviation of all 45 values of x.[2]
Mark scheme
Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.
- [M1] 439 + 470 / 45 or 909 / 45 seen.
- [A1] 50.2 (If M0 awarded, SC B1 50.2 WWW.)
- [M1] their (12405+11346) or 23751 / 45 - (their 909 / 45)²
- [A1] sd [= √119.76]=10.9 (If M0 awarded, SC B1 10.9 WWW.)
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