T Distribution Confidence Intervals Mean

Compute a 90% 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.

• (9.71, 10.29)

• (9.934, 10.066)

• (9.64, 10.36)

• (9.628, 10.372)

Using the sample above, find a 95% confidence interval for the time students typically study for a quiz.

• (36.18, 51.83)

• (36.98, 51.02)

• (35.63, 52.37)

• (34.34, 53.66)

A sample of 30 women finds the mean height to be 62.3 in and the standard deviation to be 1.5 in. Find the margin of error of women's heights with a 95% CL.

• 699

• 0.56

• 0.537

• 19.325

A 90% confidence interval for the mean speed driven by cars on East Main St. is given by (21, 45). What was the margin of error of this study?

• 12

• 24

• 33

• None of these.

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 standard deviation of $950. Construct a 99% confidence interval for the repair cost. 

• (1070, 2530)

• (1273, 2326)

• (1799, 1801)

• None of these.

I randomly select 25 students’ Math SAT scores and find the mean to be 600. I know the standard deviation of the population is 50. Find a 95% Confidence Interval.

Identify the Variables

• 50

• x-bar

• 600

• n

• 2.064

• σ

• 25

• t*

You sample 12 bugs and find the sample mean is 2.40 cm. You are told the sample standard deviation is 0.2 cm. Find a 95% Confidence Interval.

Identify the Variables

• 2.201

• t*

• 0.2

• n

• 12

• x-bar

• 2.40

• s

An IQ test was given to a simple random sample of 15 students at a certain college. The sample mean score was 105.2. Scores on this test are known to have a standard deviation of 10. It is desired to construct a 90% confidence interval for the mean IQ scores of the students at the college.

Find the critical value, t*.

• 0.90

• 1.753

• 1.761

• 2.145

I randomly select 25 students’ Math SAT scores and find the mean to be 600. I know the standard deviation of the population is 50. Find a 95% Confidence Interval.

• 95% confident the sample mean is between 580.4 and 619.6

• 95% confident the population mean is between 583.55 and 616.45

• 95% confident the population mean is between 579.36 and 620.64

• 95% confident the population mean is between 574.2 and 625.8

A sample of 30 women finds the mean height to be 62.3 in and the standard deviation to be 1.5 in. Find the margin of error of women's heights with a 95% confidence level.

• 699

• 0.56

• 0.537

• 19.325