A-LevelMathematicsProbability and statistics9709/52 · Feb/Mar 2020 · Q69 Marks
Box A contains 7 red balls and 1 blue ball. Box B contains 9 red balls and 5 blue balls. A ball is chosen at random from box A and placed in box B. A ball is then chosen at random from box B. The tree diagram below shows the possibilities for the colours of the balls chosen.
- (a)Complete the tree diagram to show the probabilities.[3]
- (b)Find the probability that the two balls chosen are not the same colour.[2]
- (c)Find the probability that the ball chosen from box A is blue given that the ball chosen from box B is blue.[4]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Feb/Mar 2020). The mark or mark type is shown in brackets.
- B1 Both correct probs, box A
- B1 2 probs correct for box B
- B1 All correct probs for box B
- M1 Two 2 factor terms added, correct or FT their 6(a).
- A1 OE
- M1 their (1/8) x (6/15) seen as numerator or denom of fraction
- M1 their (7/8) x (5/15) + (1/8) x (6/15) seen as denominator
- M1 their (7/8) x (5/15) + (1/8) x (6/15) seen as denominator
- A1
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