SOLUTION: Bulb has an average life of 600 hr. standard deviation of 30 hours. Length of bulb is approximated by a normal curve. A manager installs 10,000 bulbs. Find total number that can be

Question 771340: Bulb has an average life of 600 hr. standard deviation of 30 hours. Length of bulb is approximated by a normal curve. A manager installs 10,000 bulbs. Find total number that can be expected to last less than 687 hours.
Answer by oscargut(2103) (Show Source): You can put this solution on YOUR website!
Let X = life duration
X has a normal distribution with mean 600 and sd 30
Z = (x-600)/30 has a standard normal distribution
P(X<687) = P(Z<87/30) = P(Z<2.9) =0.99813
Then the expected number of bulbs is 10,000(0.99813) = 9981.3

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