1.A researcher wants to know how long it takes, on average, for a certain species of bacteria to divide. She watches 20 cells through a microscope and times how long it takes them to divide. She obtains the following data, in hours: 9.9, 7.5, 7.2, 8.5, 10, 7.6, 7.3, 8.7, 10.2, 9.3, 5.1, 6.3, 9.4, 10, 9, 9.5, 9.3, 8.3, 9.1, 7.5 Assuming the population standard deviation is =1.2=1.2, construct a 88% confidence interval for the average time it takes this species of bacteria to divide. a.x=_____ b. 2a=____ z2a=___ Margin of Error: E=____ We are 88% confident that this species of bacteria takes, on average, between ____hours and____ hours to divide.

2.You are interested in finding a 98% confidence interval for the average commute that non-residential students have to their college. The data below show the number of commute miles for 12 randomly selected non-residential college students. Round answers to 3 decimal places where possible.

13

14

22

23

21

11

6

18

10

26

28

11

a. To compute the confidence interval use a ? z or t? distribution.

b. With98% confidence the population mean commute for non-residential college students is between____ and_____ miles.

c.If many groups of 12 randomly selected non-residential college students are surveyed, then a different confidence interval would be produced from each group. About___ percent ?of these confidence intervals will contain the true population mean number of commute miles and about____ percent? will not contain the true population mean number of commute miles.

3. If n=101n=101, xx=41, and s=13s=13, construct a confidence interval at a 80% confidence level. Give your answers to one decimal place.

_____< < ______

4. Express the confidence interval (53.9%,69.1%) in the form of pEp. _____% %_____

5. Suppose the confidence interval (0.6358, 0.7532) represents the proportion of Skyline College students who say math is their favorite subject.

a. Based on the confidence interval, is it likely 60% of Skyline College students say math is their favorite subject?

• Yes, 0.60 is not contained in the interval
• No, 0.60 is not contained in the interval
• Yes, all the interval values are greater than 0.60

b. Based on the confidence interval, does it appear that more than 60% of Skyline College students say math is their favorite subject?

• Yes, 0.60 is not contained in the interval
• Yes, all the interval values are greater than 0.60
• No, 0.60 is not contained in the interval

c. Based on the confidence interval, does it appear that fewer than 60% of Skyline College students say math is their favorite subject?

• Yes, all the interval values are greater than 0.60
• No, 0.60 is not contained in the interval
• No, all the interval values are greater than 0.60

6. A psychologist is interested in constructing a 99% confidence interval for the proportion of people who accept the theory that a person's spirit is no more than the complicated network of neurons in the brain. 51 of the 706 randomly selected people who were surveyed agreed with this theory. Round answers to 4 decimal places where possible.

a. With 99% confidence the proportion of all people who accept the theory that a person's spirit is no more than the complicated network of neurons in the brain is between___and ____.

b. If many groups of 706 randomly selected people are surveyed, then a different confidence interval would be produced from each group. About ____percent ?of these confidence intervals will contain the true population proportion of all people who accept the theory that a person's spirit is no more than the complicated network of neurons in the brain and about____ percent? will not contain the true population proportion.

7.You want to obtain a sample to estimate a population proportion. At this point in time, you have no reasonable preliminary estimation for the population proportion. You would like to be 99% confident that you estimate is within 4% of the true population proportion. How large of a sample size is required? n = _____

8. You want to obtain a sample to estimate how much parents spend on their kids birthday parties. Based on previous study, you believe the population standard deviation is approximately =27.8=27.8 dollars. You would like to be 98% confident that your estimate is within 1 dollar(s) of average spending on the birthday parties. How many parents do you have to sample? n = _______?

9.