A-LevelMathematicsProbability and statistics9709/62 · Feb/Mar 2019 · Q15 Marks
On each day that Tamar goes to work, he wears either a blue suit with probability 0.6 or a grey suit with probability 0.4. If he wears a blue suit then the probability that he wears red socks is 0.2. If he wears a grey suit then the probability that he wears red socks is 0.32.
- (i)Find the probability that Tamar wears red socks on any particular day that he is at work.[2]
- (ii)Given that Tamar is not wearing red socks at work, find the probability that he is wearing a grey suit.[3]
Mark scheme
Marking points from the official mark scheme (Feb/Mar 2019). The mark or mark type is shown in brackets.
- [M1] Addition of 2 two-factor terms 0.6 × a + 0.4 × b
- [A1] CAO
- [B1] Correct [unsimplified] numerator seen in fraction
- [M1] 1 – their (i) as denominator in fraction
- [A1]
- [B1] Correct [unsimplified] numerator seen in fraction
- [M1] Correct or (their (i))' as denominator in fraction
- [A1]
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