Multiple choice

A factory $A$ produces $10\%$ defective valves and another factory $B$ produces $20\%$ defective. A bag contains $4$ valves of factory $A$ and $ 5$ valves of factory $B$. If two valves are drawn at random from the bag. Find the probability that at least one valves is defective. Give your answer upto two places of decimals.

  1. $0.19$
  2. $0.39$
  3. $0.29$
  4. $0.25$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The probability that a randomly selected valve is non-defective is 0.9 for factory A and 0.8 for factory B. Using the mixture of 4 valves from A and 5 from B, the probability that two selected valves are both non-defective is approximately 0.71. Thus the probability of at least one defective valve is approximately 1 - 0.71 = 0.29.

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