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A bag contains 4 white and 5 black balls. Two balls are drawn one after the other without replacement. What is the probability that the two balls drawn are of different colours?

Competition practiceData & Probability
  • A4/9
  • B40/81
  • C5/9
  • D1/2

Step-by-Step Solution

P(white then black) = (4/9)(5/8) = 20/72 and P(black then white) = (5/9)(4/8) = 20/72. Adding gives 40/72 = 5/9. With replacement the answer would be 40/81 — the second draw here depends on the first.
Answer: C) 5/9

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