Confidence Intervals for Normal and T-Distributions

A research group wishes to estimate the mean amount of time (in hours) that members of a fitness center spend exercising each week. They want to estimate the mean within a margin of error of 0.5 hours with a 95% level of confidence. Previous data suggests that the standard deviation of the population is 2.2. Which of the following is the smallest sample size they could use?

• 60

• 75

• 90

• 180

A 90% confidence interval for the average salary of all CEOs in the electronics industry was constructed using the results of a random survey of 45 CEOs. The interval was ($139,048, $154,144). Give a practical interpretation of the interval.

• 90% of the sampled CEOs have salaries that fell in the interval $139,048 to $154,144

• We are 90% confident that the mean salary of all CEOs in the electronics industry falls in the interval $139,048 to $154,144. 

• 90% of all CEOs in the electronics industry have salaries that fall between $139,048 to $154,144

• We are 90% confident that the mean salary of the sampled CEOs falls in the interval $139,048 to $154,144.

Which of the following values below represents the critical value for a 98% confidence interval for p?

• 2.326

• 2.054

• 1.645

• 3.091

A __________ gives an interval of plausible values for the _____________. 

• confidence interval, statistic

• point estimate, parameter

• point estimate, statistic

• confidence interval, parameter

Complete the equation: 
point estimate +/- _____

• standard deviation

• margin of error

• critical value

• confidence level

What critical value t* is used in constructing a 99% confidence interval based on n = 12 randomly selected observations.

• 3.106

• 3.055

• 2.576

• 1.960

Choose the appropriate confidence interval for the situation: A random sample of 30 movie theaters showed that the average price for a movie was $10 with a standard deviation of $1.20.

• One sample z interval for p

• One sample t interval for p

Choose the appropriate confidence interval for the situation: After watching a horror film, 34 out of 50 people reported problems getting to sleep.

• One sample z interval for p

• One sample t interval for p

Margin of Error is equal to:

• Standard Error

• Critical Value * Standard Error

• Critical Value

• Point Estimate

What is the margin of error for the interval (6.8, 12.9)?

• 9.85

• 3.05

• 3.50

• 6.8