Confidence Intervals Mean Use Z or T?

What is the t value associated with 90% confidence and a sample size of 15?

• 1.341
• 1.345
• 1.761
• 1.753

Which of the following does NOT have an effect on the width of a confidence interval?

• Sample mean
• t*
• Sample standard deviation
• Sample size

Which z-value is used for a 95% confidence interval?

• 1.65
• 1.96
• 2.58
• 2.33

What is the degrees of freedom equal to?

• n
• n+1
• 1-n
• n-1

Given the same mean, SD, and sample size, a confidence interval of 80% would be wider than a confidence interval of 90%

• True
• False

In a crash test of 15 troopers, collision repair costs are found to have a distribution that is approximately normal, with a mean of $1800 and a sample standard deviation of $950. Construct a 99% confidence interval for the repair cost. 

• (1069.77, 2530.23)
• (1077.13, 2522.87)
• (1167.15, 2432.85)
• None of these.

A sample of 40 people owned an average of 1.35 apple products. It is known from a previous study that the population standard deviation of apple product ownership is 0.63 products. Construct a 95% confidence interval.

• (1.11, 1.58)
• (1.15, 1.55)
• (1.19, 1.51)
• (1.09, 1.61)

A random sample of 100 visitors to a popular theme park spent an average of $142 on the trip with a sample standard deviation of $47.50. Which of the following would be the 98% confidence interval for the mean money spent by all visitors to this theme park?

• ($130.77, $153.23)
• ($130.96, $153.07)
• ($132.69, $151.31)
• ($140.88, $143.12)

A local bank needs information concerning the savings account balances of its customers. A random sample of 13 accounts was checked. The mean balance was $686.75 with a sample standard deviation of $256.20. Find a 95% confidence interval for the true mean.

• ($513.14, $860.36)
• ($525.59, $847.91) 
• ($533.27, $840.23)
• ($531.92, $841.58)

The heights (in inches) of adult males on a small Pacific Island are believed to be Normally distributed with an unknown mean μ. The average height of a random sample of 25 adult males from the island is found to be 69.72 inches, with a known population standard deviation of σ = 4.15 inches. A 99% confidence interval for μ is...

• (67.40, 72.04)
• (67.35, 72.01)
• (67.58, 71.86)
• (68.09, 71.35)