An electrical firm manufactures 100-watt light bulbs. These bulbs, according to specifications written on the package, have a mean life of 900 hours with a standard deviation of 50 hours. Assume that the distribution is symmetric about the mean. a) Give an upper bound to the probability that the life of a bulb win a new production batch will exceed 990 hours. b) Suppose that the mean is unknown but the standard deviation is 50 hours. What can be said about the probability that the life of a new bulb will be within 150 hours of the unknown mean for that batch? c) How many new bulbs should be made so as to ensure, with probability at least 0.75, that the average life would be within 25 hours of the unknown mean? Assume each bulb is produced independently.

A First Course in Probability (10th Edition)
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ISBN:9780134753119
Author:Sheldon Ross
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Chapter1: Combinatorial Analysis
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An electrical firm manufactures 100-watt light bulbs. These bulbs, according to specifications
written on the package, have a mean life of 900 hours with a standard deviation of 50 hours.
Assume that the distribution is symmetric about the mean.
a) Give an upper bound to the probability that the life of a bulb win a new production batch
will exceed 990 hours.
b) Suppose that the mean is unknown but the standard deviation is 50 hours. What can be
said about the probability that the life of a new bulb will be within 150 hours of the
unknown mean for that batch?
c) How many new bulbs should be made so as to ensure, with probability at least 0.75, that
the average life would be within 25 hours of the unknown mean? Assume each bulb is
produced independently.
Transcribed Image Text:An electrical firm manufactures 100-watt light bulbs. These bulbs, according to specifications written on the package, have a mean life of 900 hours with a standard deviation of 50 hours. Assume that the distribution is symmetric about the mean. a) Give an upper bound to the probability that the life of a bulb win a new production batch will exceed 990 hours. b) Suppose that the mean is unknown but the standard deviation is 50 hours. What can be said about the probability that the life of a new bulb will be within 150 hours of the unknown mean for that batch? c) How many new bulbs should be made so as to ensure, with probability at least 0.75, that the average life would be within 25 hours of the unknown mean? Assume each bulb is produced independently.
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