# For Academic Giant

25. You are to participate in an exam for which you had no chance to study, and for that reason cannot do anything but guess for each question (all questions being of the multiple choice type, so the chance of guessing the correct answer for each question is 1/d, d being the number of options (distractors) per question; so in case of a 4-choice question, your guess chance is 0.25). Your instructor offers you the opportunity to choose amongst the following exam formats: I. 6 questions of the 4-choice type; you pass when 5 or more answers are correct; II. 5 questions of the 5-choice type; you pass when 4 or more answers are correct; III. 4 questions of the 10-choice type; you pass when 3 or more answers are correct. Rank the three exam formats according to their attractiveness. It should be clear that the format with the highest probability to pass is the most attractive format. Which would you choose and why?

**86.** Roll two fair dice. Each die has six faces.

a. List the sample space.

b. Let A be the event that either a three or four is rolled first, followed by an even number. Find P(A).

c. Let B be the event that the sum of the two rolls is at most seven. Find P(B).

d. In words, explain what â€œP(A|B)â€ represents. Find P(A|B).

e. Are A and B mutually exclusive events? Explain your answer in one to three complete sentences, including numerical justification.

f. Are A and B independent events? Explain your answer in one to three complete sentences, including numerical justification

**112.** Table 3.22 identifies a group of children by one of four hair colors, and by type of hair.

Hair Type |
Brown |
Blond |
Black |
Red |
Totals |

Wavy |
20 |
5 |
15 |
3 |
43 |

Straight |
80 |
15 |
65 |
12 |
172 |

Totals |
100 |
20 |
80 |
15 |
215 |

b. What is the probability that a randomly selected child will have wavy hair?

c. What is the probability that a randomly selected child will have either brown or blond hair?

d. What is the probability that a randomly selected child will have wavy brown hair?

e. What is the probability that a randomly selected child will have red hair, given that he or she has straight hair?

f. If B is the event of a child having brown hair, find the probability of the complement of B.

g. In words, what does the complement of B represent?

**124**. Suppose that 10,000 U.S. licensed drivers are randomly selected.

a. How many would you expect to be male?

b. Using the table or tree diagram, construct a contingency table of gender versus age group.

c. Using the contingency table, find the probability that out of the age 20â€“64 group, a randomly selected driver is female.

**72.** You buy a lottery ticket to a lottery that costs $10 per ticket. There are only 100 tickets available to be sold in this lottery. In this lottery there are one $500 prize, two $100 prizes, and four $25 prizes. Find your expected gain or loss.

**80.** Florida State University has 14 statistics classes scheduled for its Summer 2013 term. One class has space available for 30 students, eight classes have space for 60 students, one class has space for 70 students, and four classes have space for 100 students.

a. What is the average class size assuming each class is filled to capacity?

b. Space is available for 980 students. Suppose that each class is filled to capacity and select a statistics student at random. Let the random variable X equal the size of the studentâ€™s class. Define the PDF for X. c. Find the mean of X.

d. Find the standard deviation of X.

**88.** A school newspaper reporter decides to randomly survey 12 students to see if they will attend Tet (Vietnamese New Year) festivities this year. Based on past years, she knows that 18% of students attend Tet festivities. We are interested in the number of students who will attend the festivities.

a. In words, define the random variable X.

b. List the values that X may take on.

c. Give the distribution of X. X ~ _____(_____,_____)

d. How many of the 12 students do we expect to attend the festivities?

e. Find the probability that at most four students will attend.

f. Find the probability that more than two students will attend.

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