A company manufactures a brand of light bulb with a lifetime in months that is normally distributed with mean 3 and variance 1. A consumer buys a number of these bulbs with the intention of replacing them successively as they bum out. The light bulbs have mutually independent lifetimes. Calculate the smallest number of bulbs to be purchased so that the succession of light bulbs produces light for at least 40 months with probability at least 0.9772 . (A) 14 (B) 16 (C) 20 (D) 40 (E) 55
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A company manufactures a brand of light bulb with a lifetime in months that is normally distributed with mean 3 and variance 1. A consumer buys a number of these bulbs with the intention of replacing them successively as they burn out. The light bulbs have Show more…
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A company manufactures a brand of light bulb with a lifetime in months that is normally distributed with mean 3 and variance 1. A consumer buys a number of these bulbs with the intention of replacing them successively as they burn out. The light bulbs have independent lifetimes. What is the smallest number of bulbs to be purchased so that the succession of light bulbs produces light for at least 40 months with probability at least 0.98?
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The lifetime (in hours) of a 60-watt light bulb is a random variable that has a Normal distribution with ? = 30. A random sample of 25 bulbs put on test produced a sample mean lifetime of = 1038. If in the study of the lifetime of 60-watt light bulbs it was desired to have a margin of error no larger than 6 hours with 99% confidence, how many randomly selected 60-watt light bulbs should be tested to achieve this result? A) Not within ± 2 of any of the above. B) 42. C) 13. D) 97. E) 166.
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