Practice Midterm 2 WI 10 Solutions

# The mens shirts at old navy have regular prices that

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14. The men’s shirts at Old Navy have regular prices that vary with a standard deviation of \$1.00. Today the shirts are 30% off. The standard deviation of the shirts today is: a. \$1.00 b. \$0.30 c. \$0.70 15. Suppose 5% of the U.S. population has a certain disease. Of those who have the disease, 45% are male, and 55% are female. Using this information it is possible to find the chance of having the disease for the females. a. YES b. No. You want to find P(D|F). To get this you would need P(D and F) / P(F). In the numerator you need P(D)*P(F|D), which you do have here. But in the denominator you need P(D)*P(F|D) + P(No D)*P(F|No D). You do not know P(F|No D). 16. When you are adding the numbers that appear in a single column of a two-way table you are using the Law of Total Probability. a. YES b. NO 17. If you change temperature from Fahrenheit to Centigrade the standard deviation of the temperatures will change. The conversion formula is ( 29 5 32 9 F - a. YES b. NO 3

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Problems 18-20. 63% of the U.S. population are annoyed by other people’s cell phone conversations. Of those who are annoyed, 32% have cell phones. Of those not annoyed, 51% own cell phones. 18. What is the chance that a person in the U.S. has a cell phone? 19. Choose 10 people from the U.S. at random. What is the chance that at least one of them is annoyed by other people’s cell phone conversations? 20. Choose one person from the U.S. at random. Find P(no cell phone | not annoyed). SHORT ANSWER PROBLEMS. 10 POINTS EACH. Problems 21-23. Suppose 30% of the members of Tao’s karate class are female and 70% are male. Of the males, 80% have a green belt. Of the females, 80% have a green belt. P(F) = 0.3 P(M) = 0.7 P(G|M) = 0.8 P(G|F) = 0.8 21. What percentage of all the students in Tao’s karate class have a green belt?
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