Ex 10.3.1

1. In order to estimate the average time spent on the computer terminals per student at

a university, data were collected for a sample of 81 business students over a one week

period. Assume the population standard deviation is 1.2 hours. With a 0.95 probability,

the margin of error is approximately

0.26
1.96
0.21
1.64

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2. It is known that the variance of a population equals 1936. A random sample of 121

has been taken from the population. There is a 0.95 probability that the sample mean

will provide a margin of error of

7.84 or less
31.36 or less
344.96 or less
1936 or less
None of the above answers is correct

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3. It is known that the population variance equals 484. With a 0.95 probability,

the sample size that needs to be taken if the desired margin of error is 5 or less is

25
74
189
75
None of the above answers is correct

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4. A researcher is interested in determining the average number of years employees of a

company stay with the company. If past information shows a standard deviation of 7 months,

what size sample should be taken so that at 95% confidence the margin of error will be

2 months or less

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5. If the standard deviation of the lifetime of washing machines is estimated to be 800 hours,

how large a sample must be taken in order to be 97% confident that the margin of error will

not exceed 50 hours?

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