O-LevelMathematicsProbability4024/12 · Oct/Nov 2018 · Q174 Marks
Bag A contains 3 black and 2 white beads. Bag B contains 2 black and 4 white beads. A bead is chosen, at random, from Bag A and placed in Bag B. A bead is then chosen, at random, from Bag B. [Figure of two bags with beads]
- (a)Complete the tree diagram. [Tree diagram provided with missing probabilities][2]
- (b)Find the probability that a black bead is taken from Bag B.[2]
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 (Oct/Nov 2018). The mark or mark type is shown in brackets.
- [2] 4/7 and 3/7 (black) and 5/7 (white) with two branches and both labels
- [2] 13/35 oe FT
- FT (3/5) × (4/7) + (2/5) × (their 3/7)
- or M1 for (3/5)×(4/7); or for (2/5)×(3/7)
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