A study was conducted in order to estimate μ, the mean number of weekly hours that U.S. adults use computers at home. Suppose a random sample of 81 U.S. adults gives a mean weekly computer usage time of 8.5 hours and that from prior studies, the population standard deviation is assumed to be σ = 3.6 hours.
We are 95% confident that the mean number of weekly hours that U.S. adults use computers at home is:
(a) between 8.1 and 8.9.
(b) between 7.8 and 9.2.
(c) between 7.7 and 9.3.
(d) between 7.5 and 9.5.
(e) between 7.3 and 9.7.
A study was conducted in order to estimate μ, the mean number of weekly hours that U.S. adults use computers a
95% confidence is a bit less than +/- two standard deviations. The population standard deviation must be divided by the square root of the sample size to get the sample standard deviation.
The range is thus the sample mean +/- 2(σ/sqrt(n))
8.5 +/- 2 * 3.6 / sqrt(81)
8.5 +/- (7.2 / 9)
8.5 +/- 0.8
(c) between 7.7 and 9.3
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