Unit 8 - Confidence Intervals

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

• 25

• Z

• 1.96

• n

• 600

• σ

• 50

• μ

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

Identify the Variables

• 12

• Z

• 2.40

• σ

• .2

• μ

• 1.96

• n

You sample 16 students in your school, and they average 13 hours of TV a week. Assume the standard deviation is 3. Find a 99% Confidence Interval.

Which of the following is incorrect?

• μ = 13

• σ = 3

• Z = 1.645

• n = 16

You are testing chocolate chip cookies to estimate the mean number of chips per cookie. You sample 25 cookies and you find a sample mean of 10 chips per cookie and a standard deviation of 2. Find a 95% confidence interval.

Which of the following is incorrect?

• μ = 25

• σ = 2

• Z = 1.96

• n = 25

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 580.4 and 619.6

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

You sample 16 students in your school, and they average 13 hours of TV a week. Assume the standard deviation is 3. Find a 99% Confidence Interval.

• 99% confident the population mean is between 11.77 and 14. 23

• 99% confident the population mean is between 11.53 and 14.47

• 99% confident the sample mean is between 11.06 and 14.96

• 99% confident the population mean is between 11.06 and 14.96

9 out of 25 students bring their lunch to school. Construct a 90% Confidence Interval for the proportion of students who bring their lunch to school.

What is the value of p?

• p = 9

• p = .36

• p = 2.78

• p = .64

At the State Qualifier Cross Country Meet, 45 out of 150 runners ran under 17 minutes. Construct a 99% Confidence Interval for the proportion of runners that run under 17 minutes.

What is q?

• q = 45

• q = 105

• q = .30

• q = .70

9 out of 25 students bring their lunch to school. Construct a 90% Confidence Interval for the proportion of students who bring their lunch to school.

Identify the variable

• .64

• n

• .36

• q

• 1.645

• Z

• 25

• p

At the State Qualifier Cross Country Meet, 45 out of 150 runners ran under 17 minutes. Construct a 99% Confidence Interval for the proportion of runners that run under 17 minutes.

Identify the variables

• 150

• q

• .7

• n

• 2.58

• Z

• .3

• p