A-LevelMathematicsProbability and statistics9709/52 · Feb/Mar 2020 · Q37 Marks
The weights of apples of a certain variety are normally distributed with mean 82 grams. 22% of these apples have a weight greater than 87 grams.
- (a)Find the standard deviation of the weights of these apples.[3]
- (b)Find the probability that the weight of a randomly chosen apple of this variety differs from the mean weight by less than 4 grams.[4]
Mark scheme
Marking points from the official mark scheme (Feb/Mar 2020). The mark or mark type is shown in brackets.
- M1 Using + standardisation formula, not σ², not √o, no continuity correction
- B1 AWRT ±0.772 seen B0 for ±0.228
- A1
- M1 Using ±4 used within a standardisation formula (SOI), allow σ², √o and continuity correction
- M1 Standardisation formula applied to both their ±4
- M1 Correct area 2Φ-1 oe linked to final solution
- A1
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