c) Give a 95% confidence interval for the average February charges of cardholder

Question

c) Give a 95% confidence interval for the average February charges of cardholders who charged $2000 in January Round to the nearest cent as needed.) d) From part c), give a 95% confidence interval for the average decrease in the charges of cardholders who charged $2000 in January. Round to the nearest cent as needed) e) What reservations, if any, would a researcher have about the confidence intervals made in parts c) and d)? Select all that apply. A. The data are not independent, so the confidence intervals are not valid. B. The residuals show a curvilinear pattern, so the confidence intervals may not be valid. C. The residuals show increasing spread, so the confidence intervals may not be valid D. The data are not linear, so the confidence intervals are not valid E. A researcher would not have any reservations. The confidence intervals are valid.

Explanation / Answer

c) For the given data

mean of jan=1910.20

mean of feb=1203.59

Standard deviation of Jan=2340.43

Standard deviation of Feb=1408.05

95% confidendence interval for Feb=

(1203.59-1408.05/sqrt(12),1203.59+1408.05/sqrt(12))=(406.91,2000.27)

d)

95% confidendence interval for Jan=

(1324.22-2340.43/sqrt(12),1324.22+2340.43/sqrt(12))=(585.98,3234.42)

e) option A as the data are not independent so the confidence interval are not valid

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