A researcher wishes toestimate, with 90% confidence, the population proportion of adults who think Congress is doing a good or excellent job. Her estimate must be accurate within 3% of the true proportion.

(a) No preliminary estimate is available. Find the minimum sample size needed.

(b) Find the minimum sample sizeneeded, using a prior study that found that 22% of the respondents said they think Congress is doing a good or excellent job.

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

(a) What is the minimum sample size needed assuming that no prior information isavailable?

n=

(Round up to the nearest whole number asneeded.)

(b) What is the minimum sample size needed using a prior study that found that 22% of the respondents said they think Congress is doing a good or excellentjob?

n=

(Round up to the nearest whole number asneeded.)

(c) How do the results from (a) and (b)compare?

A.

Having an estimate of the population proportion has no effect on the minimum sample size needed.

B.

Having an estimate of the population proportion reduces the minimum sample size needed.

C.

Having an estimate of the population proportion raises the minimum sample size needed.

Click to select your answer(s).

Question 2

The following data represent the concentration of dissolved organic carbon(mg/L) collected from 20 samples of organic soil. Assume that the population is normally distributed. Complete parts(a) through(c).

22.49

29.80

27.10

16.51

14.00

8.81

17.50

20.46

14.90

33.67

30.91

14.86

11.90

15.35

9.72

19.80

14.86

8.09

20.46

18.30

(a) Find the sample mean.

The sample mean is

(Round to two decimal places asneeded.)

(b) Find the sample standard deviation.

The sample standard deviation is

(Round to two decimal places asneeded.)

(c) Construct a 98% confidence interval for the population mean .

The 98% confidence interval for the population mean is

(Round to two decimal places asneeded.)