19) A system has three components in parallel with reliabilities 0.9, 0.7, and 0.6. What is the system reliability? A) 0.378 B) 0.733 C) 0.988 D) 0.985 E) 2.200 20) As the number of components in a system connected in a series increases, all other things being equal, the reliability of the system usually: A) increases. B) stays the same. C) decreases. D) increases, then decreases. E) decreases, then increases. 21) MTBF measures the average: A) calendar time between failures. B) operating time between failures. C) number of failures per unit time. D) number of operations between failures. 22) How is MTBF related to FR(N)? A) MTBF is measured in hours, while FR(N) is measured in years. B) MTBF is normally distributed, with FR(%) as its mean and FR(N) as its standard deviation. C) MTBF is the reciprocal of FR(N). D) Both MTBF and FR(N) increase when breakdown maintenance is replaced by preventive maintenance. E) MTBF and FR(N) are unrelated concepts