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Solving for Point Estimates and Confidence Intervals

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Question: The Warren County Telephone Company claims in its annual report that "the typical customer spends $70 per month on local and long-distance service." A sample of 12 subscribers revealed the following amounts spent last month.

Amounts Spent Last Month:
$64
$57
$59
$68
$60
$65
$69
$56
$58
$56
$55
$56

(a) What is the point estimate of the population mean? (Round your answer to 3 decimal places)
(b) Determine the 99% confidence interval for the population mean. (Round your answer to 2 decimal places)
Note: Confidence interval is between $ and $.
(c) Is the company's claim that the "typical customer" spends $70 per month reasonable?

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Solution Preview

Hi there, here is my explanation:

a) mean=(64+57+59+68+60+65+69+56+58+56+55+56)/12=60.250

b) Since n=12<30, we need to use a t ...

Solution Summary

The solution gives a few lines' calculations for each part with some worded explanation.

$2.19