An election poll reported that a candidate had an approval rating of 48% with a margin of error E of 3%. Construct a confidence interval for the proportion of adults who approve of the candidate.

You are a travel agent and wish to estimate, with 95% confidence, the proportion of vacationers who plan to travel outside the United States in the next 12 months. Your 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 size needed, using a prior study that found that 26% of the respondents said they planned to travel outside the United States in the next 12 months.

(c) compare the results from parts (a) and (b)

Solution Summary

The solution provides step by step method for the calculation of confidence interval and sample size for population proportion. Formula for the calculation and Interpretations of the results are also included. Interactive excel sheet is included. The user can edit the inputs and obtain the complete results for a new set of data.

The width of a confidenceinterval estimate for a proportion will be:
A. narrower for 99% confidence than for 95% confidence
B. wider for a samplesize of 100 than for a samplesize of 50
C. narrower for 90% confidence than for 95% confidence
D. narrower when the sample proportion is 0.50 than when the sample proportion is

Which of the following is not needed to be known to calculate a confidenceinterval?
a. standard deviation
b. samplesize
c. mean
d. degree of confidence

2.
A company manufactures steel bolts that continuously feed an assembly line downstream. Historically, the thickness of these bolts follows a normal distribution with a standard deviation of 1.6 mm. A recent random sample of 10 observations yielded these values of thickness, in mm:
9.7 9.9 10.3 10.1 10.5
9.4 9.9 10.1

Construct a graph determining the probability for the following problems. The sample mean and sample standard deviation are present. Construct a 90% confidenceinterval using the population mean and samplesize.

Discuss what happens to the width of the confidenceinterval as the samplesize is decreased. Discuss what happens to the width of the confidenceinterval as the confidence level is increased. Is this reasonable? Explain.

Question: A sample of 119 golfers showed that their average score on a particular golf course was 93.54 with a standard deviation of 6.16.
Answer each of the following (show all work and state the final answer to at least two decimal places):
(A) Find the 98% confidenceinterval of the mean score for all 119 golfers.
(B)

If x bar =75, S = 24, and n = 36, and assuming that the population is normally distributed, construct a 95% confidenceinterval estimate of the population mean, ยต.

Families USA, a monthly magazine that discusses issues related to health and health costs, surveyed 20 of its subscribers. It found that the annual health insurance premiums for a family with coverage through an employer averaged $10,979. The standard deviation of the sample was $1,000.
a. Based on this sample information, deve

Question 1
Sample with size n = 100 has mean = 30. Assuming the population standard deviation is 8, construct 95% confidenceinterval for population mean. Use formula on page 312, z?/2 = 1.96
Answer
between 28.4 and 31.6
between 27.0 and 33.0
between 26.1 and 34.2

You are constructing a 95% confidenceinterval using the information: n = 60, = 65.5, s = 2.5, and E = 0.7. What is the value of the middle of the interval?
A. 0.7
B. 2.5
C. 0.95
D. 65.5
What samplesize would be needed to estimate the population mean to within one-half standard deviation with 95% confidence?