A-LevelMathematicsProbability and statistics9709/63 · May/June 2025 · Q54 Marks

In Urberia, the masses, in kilograms, of men have the distribution N(70.3, 5.9²). A certain footbridge in Urberia can take a maximum safe load of 1500kg. When n men stand on the bridge, the probability that the bridge is unsafe is less than 0.01. Stating a necessary assumption, find the maximum value of n.

Mark scheme

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

[B1] OE. Allow: assume that all the men on the bridge are independent of one another.
[M1] Must have square root n. Allow wrong z but must be a z value.
[A1] Correct quadratic equation or inequality in square root n. OE.
[A1] CWO.

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Topic: Probability and statistics, A-Level Mathematics (syllabus 9709). Structured question, 4 marks.
Source: A-Level Mathematics, May/June 2025 Paper 6 Variant 3, question 5.

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