A-LevelMathematicsProbability and statistics9709/62 · May/June 2018 · Q46 Marks

Mrs Rupal chooses 3 animals at random from 5 dogs and 2 cats. The random variable X is the number of cats chosen.

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[B1] (i) Prob distribution table drawn, top row correct with at least one probability 0 < p < 1 entered, condone additional values with p = 0 stated
[B1] (i) One probability correct (need not be in table)
[B1] (i) Another probability correct (need not be in table).
[B1] (i) Values in table, all probs correct (to 3SF) or 3 probabilities summing to 1
[M1] (ii) Unsimplified correct numerical expression for variance or their probabilities from (i) 0 < p < 1 in unsimplified variance expression
[A1] (ii) Correct answer (0.40816...) nfww Final answer does not imply the method mark

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Topic: Probability and statistics, A-Level Mathematics (syllabus 9709). Structured question, 6 marks.
Source: A-Level Mathematics, May/June 2018 Paper 6 Variant 2, question 4.

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