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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 at least one bulb is good.

Correct answer: C. 125/126

  • A. 6/63
  • B. 2/63
  • C. 125/126
  • D. 1/126

Explanation

The complement of at least one good bulb is selecting all four defective bulbs. That probability is C(4,4)/C(9,4) = 1/126, so the required probability is 1 - 1/126 = 125/126. The likely wrong choice is 1/126, which gives the probability of all defective rather than at least one good.

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