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​Q27: Answers – Paper 3 – June 2018
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A bag contains 30 discs.
10 are red and 20 are blue.
  • One disc is taken out at random and replaced by two of the other colour.
  • Another disc is then taken out at random and replaced by two of the other colour.
  • Another disc is then taken out at random.

Work out the probability that all three discs taken out are red.
Question
27) A bag contains 30 discs.
10 are red and 20 are blue.
  • One disc is taken out at random and replaced by two of the other colour.
  • Another disc is then taken out at random and replaced by two of the other colour.
  • Another disc is then taken out at random.

Work out the probability that all three discs taken out are red.
[3 marks]