A-LevelMathematicsProbability and statistics9709/62 · Feb/Mar 2017 · Q23 Marks

A bag contains 10 pink balloons, 9 yellow balloons, 12 green balloons and 9 white balloons. 7 balloons are selected at random without replacement. Find the probability that exactly 3 of them are green.

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2017). The mark or mark type is shown in brackets.

[M1] Using combinations with attempt to evaluate 2 terms in num. and 1 in denom.
[M1] Correct numerator or denominator unsimplified
[A1] = 0.242
[M1] Multiplying 3 green probs with 4 non-green probs, without replacement
[M1] Multiplying by 7C3
[A1] = 0.242

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Topic: Probability and statistics, A-Level Mathematics (syllabus 9709). Structured question, 3 marks.
Source: A-Level Mathematics, Feb/Mar 2017 Paper 6 Variant 2, question 2.

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