The capacities (in ampere-hours) were measured for a sample of 120 batteries. The

Chapter 5, Problem 7

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The capacities (in ampere-hours) were measured for a sample of 120 batteries. The average was 178 and the standard deviation was 14.

a. Find a $95 \%$ confidence interval for the mean capacity of batteries produced by this method.

b. Find a $99 \%$ confidence interval for the mean capacity of batteries produced by this method.

c. An engineer claims that the mean capacity is between 176 and 180 ampere-hours. With what level of confidence can this statement be made?

d. Approximately how many batteries must be sampled so that a95%confidence interval will specify the mean to within $\pm 2$ ampere-hours?

e. Approximately how many batteries must be sampled so that a $99 \%$confidence interval will specify the mean to within $\pm 2$ ampere-hours?

Equation Transcription:

$95\%$

$99\%$

$\pm{}2$

$99\%$

$\pm{}2$

Text Transcription:

95%

99%

\pm 2

99%

\pm 2

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