1. In order to estimate the proportion of office workers who listen to streamed music on a work computer on a regular basis, a sample of 1200 office workers who work at a computer was taken. Of them, 543 listen to steamed music on the computer at work. A 99% confidence interval for the proportion of all office workers who listen to streamed music at work is about:
The mean monthly salary of a random sample of 20 college graduates under the age of 30 was found to be $3120 with a standard deviation of $67. Assume that the distribution of salaries for all college graduates under the age of 30 is normally distributed.
(a) Construct a 90% confidence interval for the population mean of monthly salaries of all college graduates under the age of 30.
(b) All other information remaining unchanged, which of the following will produce a wider interval than the 90% confidence interval constructed above?
A sample with a standard deviation of 52 instead of 67
An 80% confidence interval rather than a 90% confidence interval
A sample of size 28 instead of 20
A sample of size 24 instead of 20
A sample with a standard deviation of 72 instead of 67
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