Confidence interval, error of estimate, sample size

In the publication Employment and Earnings, information on the ages of people in the civilian labor force was published. Seventy-five people in the civilian labor force are randomly selected. The mean age is 37.4 years with a standard deviation of 10.3 years.

a. Find the 99% confidence interval for the mean age.
b. What is the error of estimate for the 90% confidence interval?
c. What is the minimum sample size that is needed for the 95% confidence interval, if the maximum error of estimate is 2.1 years?

Solution Preview

a. Find the 99% confidence interval for the mean age.

Mean=M =37.4years

Standard deviation =s=10.3years

sample size=n=75

sx=standard error of mean=s/square root of n=1.1893= ( 10.3 /square root of 75)

Confidence level=99%

a (alpha) =1%=100% -99%

or Significance level=a (alpha) =0.01(expressed as a number )

No of tails=2

Since sample size=75>=30use normal distribution

Z at the ...

Solution Summary

The solution calculates confidence interval of the mean age, error of estimate for for the confidence interval and sample size for the confidence interval.

Assume that a sample is drawn and z(±/2) = 1.96 and ? = 20. Answer the following questions:
(A) If the Maximum Error of Estimate is 0.02 for this sample, what would be the samplesize?
(B) Given that the sampleSize is 400 with this same z(?/2) and Ï?, what would be the Maximum Error of Estimate?
(C) What happens

I need help solving 95% confidence interval and point estimate problems.
A sample of 16 people are used, each one is to keep track of their time with the following result in hours.
1.8, 1.7, 0.9, 1.1, 1.5, 1.5, 1.2, 0.6, 1.4, 0.9, 0.7, 1.8, 1.7, 2.2, 1.5, 1.3
Construct a 95% confidence interval for the amount of time n

Assume that a sample is drawn and z(?/2) = 1.96 and Ï? = 15. Answer the following questions:
(A) If the Maximum Error of Estimate is 0.04 for this sample, what would be the samplesize?
(B) Given that the sampleSize is 400 with this same z(?/2) and Ï?, what would be the Maximum Error of Estimate?
(C) Wha

1. Use the information given to calculate the standard error of the mean. Mean systolic blood pressure for a sample of n=324 men is =123.5, and the standard deviation is s=9.
2. If each of the following is decreased but everything else remains the same, will a confidence interval become wider, will it become narrower, or wil

A manufacturer wishes to estimate the reliability (in months) of a certain product. An estimate of the population standard deviation from a previous sample was 12 months. If the manufacturer desires to be within 4 months of the true value with approximately 80% confidence, what should the samplesize be?

The manager of a department store wants to determine what proportion of people who enter the store use the store's credit cards for their purchases. What sizesample should he take so that at 95% confidence the error will not be more than 6%?

A sample of n=16 scores is obtained from an unknown population. The sample has a mean of M=46 with SS=6000.
a. Use the sample data to make an 80% confidence interval estimate
of the unknown population mean.
b. Make a 90% confidence interval estimate of μ.
c. Make a 95% confidence interval estimate of μ.

You are constructing a 95% confidence interval 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?

The width of a confidence interval 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

Can you show how to do this in Excel if possible?
Question:
1. A scientist wants to estimate the proportion of plants with berries growing in a particular region. They want to be within 6% of the true proportion when using a confidence interval of 99%.
How many plants must be sampled if no preliminary estimate is avai