Suppose that there is a chance for a newly constructed building to collapse, whether the design is faulty or <strong>NOT</strong>. The chance that the design is faulty is 10%. The chance that the building collapses is 95% if the design is faulty, otherwise it is 45%. If it is seen that the building has collapsed, then what is the probability that it is due to faulty design?

  1. A. 0.10
  2. B. 0.19
  3. C. 0.45
  4. D. 0.95

Correct Answer: B. 0.19

Explanation

Let F be the event of faulty design, C be the event of collapse. P(F) = 0.10, P(F') = 0.90. P(C|F) = 0.95, P(C|F') = 0.45. By Bayes' Theorem, P(F|C) = \frac{P(C|F)P(F)}{P(C|F)P(F) + P(C|F')P(F')} = \frac{0.95 \times 0.10}{0.95 \times 0.10 + 0.45 \times 0.90} = \frac{0.095}{0.095 + 0.405} = \frac{0.095}{0.500} = 0.19.

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