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Statistics - Study Guide 2 Questions

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1. Which of the following statement(s) about the normal probability distribution is/are true?

a. The mean equals the mode and the median
b. The median equals the mode
c. The mean divides the distribution into two equal parts
d. All of the above
e. None of the above


a. 375 and 425
b. 300 and 500
c. 390 and 410
d. 275 and 525
e. 380 and 420

3. The automobile club performed a survey and discovered that 80% of drivers in Delaware wear seatbelts. A sample of 10 drivers was selected. What is the probability that at least 5 wore seatbelts?

The above situation describes:
a. Binomial
b. Continuous distribution
c. Cannot tell from the information given
d. None of the above

4. A survey of college statistics professors showed an average salary of $42,000 per year with a standard deviation of $6,000. What percent of statistics professors earn between $36,000 and $48,000?

a. 85%
b. 95%
c. 68%
d. None of the above

5. According to a sampling plan, 20 incoming widgets are to be checked and if 2 or less defective widgets are found, the lot will be accepted. If an incoming lot is 10 percent defective, what is the probability of accepting the lot?

The above situation describes:
a. 0
b. 1
c. 0.323
d. 0.667
e. None of the above

6. State the main points of the Central Limit Theorem for a mean.

7. Why is population shape of concern when estimating a mean? What does sample size have to do with it?

8. A random sample of 10 miniature Tootsie Rolls was taken from a bag. Each piece was weighed on a very accurate scale. The results in grams were

3.087 3.131 3.241 3.241 3.270 3.353 3.400 3.411 3.437 3.477

a) Construct a 90 percent confidence interval for the true mean weight. (b) What sample size would be necessary to estimate the true weight with an error of ± 0.03 grams with 90 percent confidence? (c) Discuss the factors which might cause variation in the weight of Tootsie Rolls during manufacture.

9. In 1992, the FAA conducted 86,991 pre-employment drug tests on job applicants who were to be engaged in safety and security-related jobs, and found that 1,143 were positive.(a) Construct a 95 percent confidence interval for the population proportion of positive drug tests. (b) Why is the normality assumption not a problem, despite the very small value of p?

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