A-LevelMathematicsProbability and statistics9709/51 · Oct/Nov 2020 · Q14 Marks

Two ordinary fair dice, one red and the other blue, are thrown. Event A is 'the score on the red die is divisible by 3'. Event B is 'the sum of the two scores is at least 9'.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

[M1] Complete outcome space or or listing A and B outcomes or listing ANB outcomes
[A1] With evidence. P(A∩B) = 5/36
[M1] Their 1/3 x their 10/36 seen (for P(A) x P(B))
[A1] P(A) × P(B) and P(A∩B) seen in workings and correct conclusion stated. Condone 5/36 being stated in (a)
[M1] (Alternative) OE, their P(A∩B) / their P(A) seen (for P(B|A))
[A1] (Alternative) P(A/B), P(B), 5/12, 5/18 seen in workings and correct conclusion stated. Condone 5/36 being identified in (a)

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Topic: Probability and statistics, A-Level Mathematics (syllabus 9709). Structured question, 4 marks.
Source: A-Level Mathematics, Oct/Nov 2020 Paper 5 Variant 1, question 1.

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