1. Assuming a mean (point estimate) of 120, standard deviation of 18, sample size of 81 and a 95% confidence level. Find:
2. Standard error (4 marks)
3. Margin of error (4 marks)
4. Confidence interval estimate (4 marks)

1. XYZ Company is considering a sample study with the following ten (10) values:

23	25	26	28	28
29	31	34	40	40

1. Determine the mean (x) value (4 marks)
2. Calculate the standard deviation (maintain 2 decimal point) (6 marks)
3. Given a 95% confidence level, construct a confidence interval estimate (12 marks)

1. Identify:
   1. The critical value of z given 99% confidence level (2 marks)
   2. The critical value of t given 80% confidence level and df = 20

(2 marks)

1. The critical value of t given 90% confidence level and sample size of 22 (2 marks)
2. The critical value of z given 89.9 confidence level (2 marks)
3. The critical value of z given 75% confidence level (2 marks)

1. Assume a 95% confidence level, standard deviation of 40, and a margin of error of 2.5. what sample size should the researcher use in his research work? (6 marks)