6. (a) Amanufacturer of light bulbs advertises that, c 5,000 hours. Assume that the lifetime of a ram deviation of 400 hours. A statistician took a each bulb, the amount of time until the bull

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Q6. (a) A manufacturer of light bulbs advertises that, on average, its long-life bulb will last for more than
5,000 hours. Assume that the lifetime of a randomly selected bulb of this type has a standard
deviation of 40o hours. A statistician took a random sample of 100o bulbs and measured, for
each bulb, the amount of time until the bulb burned out. The sample mean is 5,065 hours.
Find a 95% confidence interval for the expected number of hours a randomly selected bulb of
this type will last.
(b) The statistician has drawn another sample of size n. However, the information about the sample
mean is lost after obtaining a 1 – a confidence interval for the expected number of hours a
randomly selected bulb of this type will last, which is [5, 030, 5, 070].
(i) Find the sample mean.
(ii) If the statistician would like to obtain a 90% confidence interval for the expected number
of hours a randomly selected bulb of this type will last and keep the maximum deviation
from the sample mean to be 50 hours, what should be the minimum value of n?
(iii) If the sample of size 1,000 is obtained and the statistician would like to obtain a 99% con-
fidence interval for the expected number of hours a randomly selected bulb of this type
will last, what is the width of the interval?
(iv) If the statistician has obtained the sample with size 3o0 and eventually agree with the light
bulbs manufacturer's claim, what is the maximum confidence coefficient the statistician
applied?
(c) The statistician found that the assumption on the standard deviation is incorrect. Therefore,
the standard deviation is now an unknown. Find a 95% confidence interval for the expected
number of hours a randomly selected bulb of this type will last if
(i) the sample size, sample mean, the second sample moment are 100, 5,065 hours and 25814225
respectively.
(ii) the statistician took a random sample with size 10,000 and found out that the sample mean
and the sample standard deviation are 5,065 and 400 hours respectively.
Transcribed Image Text:Q6. (a) A manufacturer of light bulbs advertises that, on average, its long-life bulb will last for more than 5,000 hours. Assume that the lifetime of a randomly selected bulb of this type has a standard deviation of 40o hours. A statistician took a random sample of 100o bulbs and measured, for each bulb, the amount of time until the bulb burned out. The sample mean is 5,065 hours. Find a 95% confidence interval for the expected number of hours a randomly selected bulb of this type will last. (b) The statistician has drawn another sample of size n. However, the information about the sample mean is lost after obtaining a 1 – a confidence interval for the expected number of hours a randomly selected bulb of this type will last, which is [5, 030, 5, 070]. (i) Find the sample mean. (ii) If the statistician would like to obtain a 90% confidence interval for the expected number of hours a randomly selected bulb of this type will last and keep the maximum deviation from the sample mean to be 50 hours, what should be the minimum value of n? (iii) If the sample of size 1,000 is obtained and the statistician would like to obtain a 99% con- fidence interval for the expected number of hours a randomly selected bulb of this type will last, what is the width of the interval? (iv) If the statistician has obtained the sample with size 3o0 and eventually agree with the light bulbs manufacturer's claim, what is the maximum confidence coefficient the statistician applied? (c) The statistician found that the assumption on the standard deviation is incorrect. Therefore, the standard deviation is now an unknown. Find a 95% confidence interval for the expected number of hours a randomly selected bulb of this type will last if (i) the sample size, sample mean, the second sample moment are 100, 5,065 hours and 25814225 respectively. (ii) the statistician took a random sample with size 10,000 and found out that the sample mean and the sample standard deviation are 5,065 and 400 hours respectively.
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