#25

A researcher wishes to estimate, with 90% confidence, the population proportion of adults who think Congress is doing a good or excellent job. Her estimate must be accurate within 5% of the true proportion.

(a) No preliminary estimate is available. Find the minimum sample size needed. (round to the nearest whole number)

(b) Find the minimum sample size needed, using a prior study that found that 36% of the respondents said they think Congress is doing a good or excellent job.

(c) Compare the results from parts (a) and (b).

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#28

The number of hours of reserve capacity of

10

randomly selected automotive batteries is shown to the right.

1.74	1.86	1.59	1.69	1.71
1.97	1.37	1.57	1.46	2.03

Assume the sample is taken from a normally distributed population. Construct 98% confidence intervals for (a) the population variance 2 and (b) the population standard deviation .

a) ) The confidence interval for the population variance is _______ (round to three decimal places as needed)

b) The confidence interval for the population standard deviation is _______ (round to three decimal places as needed.)