Calculating Critical Value for Confidence Intervals

A study of a large local high school tried to determine the mean amount of money that each student had saved. The study surveyed a random sample of 97 AP students in the high school and found a mean savings of 4100 dollars with a standard deviation of 500 dollars. What would be the critical value for a 90% confidence interval in this situation?

A study of a local high school with 2,000 students tried to determine the mean number of text messages that each student sent per day. The study surveyed a random sample of 253 students in the high school and found a mean of 186 messages sent per day with a standard deviation of 65 messages. What would the critical value for an 80% confidence interval be in this situation?

A survey was given to a random sample of 55 residents of a town of 30,000 people to determine whether they support a new plan to raise taxes in order to increase education spending. Of those surveyed, 22 respondents said they were in favor of the plan.

What would be the critical value for a 95% confidence interval?

A survey was given to a random sample of 1750 voters in the United States to ask about their preference for a presidential candidate. Of those surveyed, 595 respondents said that they preferred Candidate A.

What would the critical value for a 99% confidence interval be for this situation?

The z-score number used for calculating a 95% confidence interval is:

• 1.65

• 1.96

• 2.58

• 0.90

What is the confidence interval being calculated in the image to the left?

• 90% confidence interval

• 95% confidence interval

• 99% confidence interval

• 35% confidence interval

The z-score number used for calculating a 90% confidence interval is:

• 1.65

• 1.96

• 2.58

• 0.90

A study by the department of education of a certain state was trying to determine the mean SAT scores of the graduating high school seniors. The study examined the scores of a random sample of 25 graduating seniors and found the mean score to be 471 with a standard deviation of 83.

What would the critical value for a 98% confidence interval be in this situation?

The critical _____ is a multiplier that makes the interval wide enough to have the stated capture rate.

Find the Critical Value for a confidence level of 82%.