Reliability

What is the reliability of a system with two parts of reliability 0.9 connected in parallel, which functions if either one works?

  1. A0.81
  2. B0.9
  3. C0.99
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Answer: C. 0.99

A parallel system fails only when both parts fail. The probability of that is (1 − 0.9) × (1 − 0.9) = 0.01, so the reliability is 1 − 0.01 = 0.99. This shows that redundancy can improve reliability.

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