A-LevelMathematicsProbability and statistics9709/51 · May/June 2025 · Q13 Marks

The masses of the bags of rice made by a company are normally distributed with mean μkg and standard deviation 0.14kg. The probability that the mass of a randomly chosen bag of this rice is less than 1.48 kg is 0.22. Find the value of μ.

Mark scheme

Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.

[B1] 0.771 < z < 0.773 or -0.773 < z < -0.771 seen.
[M1] Use of the standardisation formula with μ, 1.48 and 0.14 and equating to a z-value (not 0.78, 0.22, 0.5871, 0.7823, 0.228). Condone σ², √σ and continuity correction ±0.005.
[A1] 1.585 < μ ≤ 1.59. If M0 scored SC B1 for correct answer WWW.

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Topic: Probability and statistics, A-Level Mathematics (syllabus 9709). Structured question, 3 marks.
Source: A-Level Mathematics, May/June 2025 Paper 5 Variant 1, question 1.

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