Question

The life of a semiconductor laser at a constant power is normally distributed with a mean...

The life of a semiconductor laser at a constant power is normally distributed with a mean of 8000 hours and a standard deviation of 400 hours.

(i) What is the probability that a laser fails before 7500 hours?

(ii) What is the life in hours that 85% of the lasers exceed?

(iii) If four lasers are used in a product and they are assumed to fail independently, what is the probability that at least one fail before 7000 hours?

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