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A box contains nine bulbs out of which 4 are defective. If four bulbs are chosen at random, find the probability that all the four bulbs are defective.

Correct answer: D. 1/126

  • A. 62/63
  • B. 125/126
  • C. 1/63
  • D. 1/126

Explanation

To select all four defective bulbs, there is C(4,4) = 1 favorable selection. The total ways to select four bulbs from nine are C(9,4) = 126, so the probability is 1/126. Students may choose 125/126 by calculating the complementary event, at least one good bulb.

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