# Probability Problem Set

Problem 3

a. A random sample of 25 was drawn from a normal distribution with a standard deviation of 5. The sample mean is 80. Determine the 95% confidence interval estimate of the population mean.

b. Repeat part (a) with a sample size of 100.

c. Repeat part (a) with a sample size of 400.

d. Describe what happens to the confidence interval estimate when the sample size increases.

Problem 4

a. A statistics practitioner randomly sampled 100 observations from a population with a standard deviation of 5 and found that is 10. Estimate the population mean with 90% confidence.

b. Repeat part (a) with a sample size of 25.

c. Repeat part (a) with a sample size of 10.

d. Describe what happens to the confidence interval estimate when the sample size decreases.

https://brainmass.com/statistics/confidence-interval/probability-problem-set-510954

#### Solution Preview

3. a) The critical value for 95% confidence interval is 1.96.

a.margin of error=1.96*5/sqrt(25)=1.96

upper limit: 80+1.96=81.96

lower limit: 80-1.96=78.04

Therefore, 95% confidence interval is [78.04, 81.96].

b) margin of error=1.96*5/sqrt(100)=0.98

upper limit: 80+0.98=80.98

lower limit: ...

#### Solution Summary

The solution assists with answering the probability problem set.