STAT225 QUIZ 1 Spring 2015

NAME_____________________________

INSTRUCTIONS

· The quiz is worth 75 points total.

· The quiz covers Chapters 1, 2 and 3 in Lane et al and chapters 1 and 2 in Illowsky et al.

· The quiz is open book and open notes. This means that you may refer to your textbook, notes, and online course materials, but you must work independently and may not consult anyone. The brief honor statement is on top of the exam. If you fail to put your name under the statement, your quiz will not be accepted. You may take as much time as you wish, provided you turn in your quiz via LEO assignments folder by 11:59 pm EDT on Sunday, April 5, 2015.

(For Questions 1 to 7) The checkout times (in minutes) for 12 randomly selected customers at an electronic store during the store’s busiest time are as follows:

5.0

8.4

6.0

8.0

11.0

9.5

12.7

6.5

10.0

9.0

6.5

13.0

1. (5 points) (Show work) What is the mean checkout times based on the 12 checkout times. (Round the answers to two decimal places)

2. (10 points) (Show work) Give a 5-number summary of the checkout time. (Round the answers to two decimal places)

3. (5 points) Prepare a frequency distribution with a class width of 2 minutes (with the first class as 4.0 – 5.9, etc.).

4. (5 points) (Show work) Identify the class midpoints for frequency distribution from Question 3. (Round the answers to two decimal places)

5. (5 points) (Show work) Construct the relative frequency distribution based on the frequency distribution from Question 3. (Round the percentage to one decimal place)

6. (5 points) (Show work) We usually find the mean checkout time based on the raw data. Now suppose that we don’t have the raw data, but instead, we only have the frequency distribution. Find the mean checkout time based on the frequency distribution from Question 3. (Round the answer to two decimal places) Compare your results with the "actual" mean checkout time you found in Question 1.

7. (10 points) (Show work) Find the standard deviation of the checkout time based on the frequency distribution from Question 3. Please show your calculation in the following table. (Round the answer to two decimal places)

Check-out time

Frequency f

Mid-point x

x2

f * x2

f * x

4.0 – 5.9

Sum

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(For Questions 8, 9 & 10) To qualify for a mortgage, an applicant needs to have a good FICO credit score. We chose a random sample of 6 applicants from a local bank, and their FICO scores are 710, 740, 655, 810, 560 and 600.

8. (10 points) (Show work) What is the standard deviation of the FICO scores in the sample? Please show your calculation in the following table; you may not need all columns based on the formula you use. (Round the answer to two decimal places)

FICO Score x

x2

x-mean

(x-mean)2

710

740

655

810

560

600

Sum

9. (5 points) (Show work)Are any of these FICO scores considered unusual in the sense of our textbook? Explain.

10. (5 points) (Show work) What is the coefficient of variation in FICO scores of the sample? (Round the answer to two decimal places)

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11. (5 points) Determine whether the given value is a parameter or statistics. Please explain your answer.

(a) An agency conducts a survey on the choice of fruit by Americans. It is reported by the agency that 61% of the respondents prefers apple.

(b)A STAT 200 instructor randomly selected 200 students and found the average study time is 25.2 hours per week.

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12. (5 points) John is a recent college graduate, who is considering a possible career in the engineering. One factor that will affect her decision is how much money he is likely to make. He got salary information from Internet. Since you are taking a Statistics course, he would like to get your opinion on whether mean salary or median salary information is more useful for her. What would be your recommendation? Please explain your answer.