1. 1. Solve E = 1
305 .
ANSWER
0.057 n . 1
2. Solve =
ANSWER
1600

2. 3. The mean score on an exam was 78. You scored
3. The mean score on an exam was 78. You scored within 5 points of the mean. If x = represents your possible score x on the exam, what is the range of your score? –
ANSWER
73 ≤ x ≤ 83

3. EXAMPLE 1
Classify samples
Baseball
A sportswriter wants to survey college baseball coaches about whether they think wooden bats should be mandatory throughout college baseball. Identify the type of sample described.
The sportswriter contacts only the coaches that he has cell phone numbers for in order to get quick responses.
The sportswriter mails out surveys to all the coaches and uses only the surveys that are returned.

4. EXAMPLE 1
Classify samples
SOLUTION
The sportswriter selected coaches that are easily accessible. So, the sample is a convenience sample.
The coaches can choose whether or not to respond. So, the sample is a self-selected sample.

5. EXAMPLE 2
Identify a biased sample
Concert Attendance
The manager of a concert hall wants to know how often people in the community attend concerts. The manager asks 50 people standing in line for a rock concert how many concerts per year they attend. Tell whether the sample is biased or unbiased. Explain your reasoning.
SOLUTION
The sample is biased because people standing in line for a rock concert are more likely to attend concerts than people in general.

6. EXAMPLE 3
Choose an unbiased sample
Senior Class Prom
You are a member of the prom committee. You want to poll members of the senior class to find out where they want to hold the prom. There are 324 students in the senior class. Describe a method for selecting a random sample of 40 seniors to poll.
SOLUTION
STEP 1
Make: a list of all 324 seniors. Assign each senior a different integer from 1 to 324.

7. EXAMPLE 3
Choose an unbiased sample
STEP 2
Generate: 40 unique random integers from 1 to 324 using the randInt feature of a graphing calculator. The screen at the right shows six such random integers.
If while generating the integers you obtain a duplicate, discard it and generate a new, unique integer as a replacement.
STEP 3
Choose: the 40 students that correspond to the 40 integers you generated in Step 2.

8. YOU TRY
for Examples 1, 2, and 3
SCHOOL WEBSITE: A computer science teacher wants to know if students would like the morning announcements posted on the school’s website. He surveys students in one of his computer science classes. Identify the type of sample described, and tell whether the sample is biased.
SOLUTION
The computer science teacher surveys students in one of his computer science classes where students are easy to reach. So, the sample is a convenience sample. The sample is biased as the students of only the computer class are surveyed.

9. YOU TRY
for Examples 1, 2, and 3
WHAT IF? In Example 3, what is another method you could use to generate a random sample of 40 students? 2.
SOLUTION
Place each student’s name on a small piece of paper in a hat and draw 40 names.

10. EXAMPLE 4
Find a margin of error
MEDIA SURVEY
In a survey of 1011 people, 52% said that television is their main source of news.
What is the margin of error for the survey?
Give an interval that is likely to contain the exact percent of all people who use television as their main source of news.

11. Use the margin of error formula.
EXAMPLE 4
Find a margin of error
SOLUTION
Use the margin of error formula. + – n 1 =
Margin of error
Write margin of error formula. + –
1011 1 =
Substitute 1011 for n.
0.031 + –
Use a calculator.
ANSWER
The margin of error for the survey is about %. + –

12. EXAMPLE 4
Find a margin of error
To find the interval, subtract and add 3.1% to the percent of people surveyed who said television is their main source of news (52%).
52% – 3.1%
= 48.9%
52% + 3.1%
= 55.1%
ANSWER
It is likely that the exact percent of all people who use television as their main source of news is between 48.9% and 55.1%.

13. Use the Margin of Error Formula
EXAMPLE 5
Use the Margin of Error Formula
SOLUTION
Use the margin of error formula. + – 1 n =
Margin of error
Write margin of error formula.
0.05 + – = 1 n
Substitute for margin error.
0.05 + –
0.0025 = 1 n
Square each side.
n =
Solve for n.
There were 400 people surveyed.
ANSWER
The correct answer is C. A B C D

14. The margin of error for the survey is about 2.9%.
YOU TRY
for Examples 4 and 5
INTERNET: In a survey of 1202 people, 11% said that they use the Internet or more than 10 hours per week. What is the margin of error for the survey? How many people would need to be surveyed to reduce the margin of error to 2%? + – 3.
SOLUTION + – n 1 =
Margin of error
Write margin of error formula. + –
1202 1 =
Substitute 1202 for n.
0.029 + –
Use a calculator.
The margin of error for the survey is about %. + –

15. Use the margin of error formula.
YOU TRY
for Examples 4 and 5
Use the margin of error formula. + – 1 n =
Margin of error
Write margin of error formula. =
0.02 + – 1 n
0.05
Substitute for margin error. + –
0.0004 = 1 n
Square each side.
n =
Solve for n.
2500 people need to be surveyed.
ANSWER

16. KEEP GOING
1. A cafeteria buys grated cheese from a food service.
The cheese is packed in boxes labeled 10 pounds. To
test that the weight is correct, the cafeteria manager
weighs the first 5 boxes in a recent order.
a. Identify the type of sample and explain why it is
biased.
ANSWER
Convenience; the sample may be biased if the same production line packed the first 5 boxes and other lines packed other boxes.

17. KEEP GOING
b. In a random sample of 550 boxes, 52% weighed more than 10 pounds. Give the interval that is likely to contain the exact percent that weighed over 10 pounds. How many boxes would need to be weighed if the margin of error was 3.8%?
between 47.7% and 56.3%; 694 boxes
ANSWER