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The life of a ventilator is normally distributed with a mean of 9000 hours and a...

The life of a ventilator is normally distributed with a mean of 9000 hours and a standard deviation of 500 hours.

(a) What is the probability that the ventilator fails before 8000 hours?

(b) What is the life in hours that is exceeded by 96% of the ventilators?

(c ) If 20 such ventilators are used in a hospital, and they are assumed to fail independently, what is the probability that all 20 are still operating after 7500 hours?

Math   Statistics-And-Probability   
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