Nine times out of ten, seniors will have an average score within 5% of 75%.
We can rewrite this statement as:
Nine times out of ten or 90% of the times, seniors will have an average score within 5% of 75% i.e from 70% to 80%.
Thus we can say, the exam creator is 90% confident that the seniors will have an average score between 70% to 80%.
From here we can conclude that the Confidence Level is 90%.
Margin of error means by how much points the population parameters will vary from the sample mean/sample proportion. We are provided this information in the question:
Seniors will have an average score within 5% of 75%.
Thus the margin of Error will be 5% and the sample proportion is 75%.
So the Confidence Interval is 75-5 to 75+5 i.e 70% to 80%
The exam creator is 90% confident that the seniors will have an average scores between 70% to 80%
