Problem 830

A field test for a new exam was given to randomly selected seniors. The exams were graded, and the sample mean and sample standard deviation were calculated. Based on the results, the exam creator claims that on the same exam, nine times out of ten, seniors will have an average score within 5% of 75%.

Is the confidence interval at 90%, 95%, or 99%? What is the margin of error? Calculate the confidence interval and explain what it means in terms of the situation.




nine times out of ten, so confidence interval is 90%
margin of error = (75-5)/2 = 35% = 0.35
90% confidence interval means we have 90% of population proportion is lies between 5% to 75%.



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