The life of a semiconductor laser at a constant power is normally distributed Wi

Question

The life of a semiconductor laser at a constant power is normally distributed With a mean of 7000 hours and a standard deviation of 600 hours What is the probability that a laser fails before 5:800 hours? What is the life in hours that 90% of the lasers exceed? A random sample of 9 structural elements is tested for compressive strength. We know that the true mean compressive strength mu = 5500 psi and the standard deviation is sigma = 100 psi. Find the probability that the sample mean compressive strength exceeds 4985 psi.

Explanation / Answer

1) a)mean = = 7000 standard deviation , = 600 P(X-3.36)=1-0.0004 = 0.9996 hence probability that sample mean compressive strength exceeds4985 psi is 0.9996

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