AP Stats Critical Value

Find the critical value, z*, for 91% confidence.

• 70

• 1.34

• 0.18

• -1.34

Identify the confidence interval used in the figure below if each shaded area is equal to 0.05.

• 90%

• 95%

• 98%

• 99%

Find the value of z* for a 90% confidence interval.

• -1.96

• 1.645

• 1.440

• -1.598

Find the critical value, z* for 97%

• 1.88

• 2.17

• -1.88

• -2.17

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 high school students 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? round to 3 decimals.

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?

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 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? Round to 3 decimals.

You want to compute a 90% confidence interval for the mean difference in height for mothers and their adult daughters using a random sample of 30 mothers who have an adult daughter. What critical value should you use for this interval? (Enter 3 decimal places)

Answer explanation

The 𝑡* value for 90% confidence and df = 29 is 𝑡* = 1.699.