Random Variables and Distributions

The table above shows a television station's advertisement sales. The distribution of sales for one 24-hour day is given. Solve for the standard deviation. Round to the nearest hundredth.

• 35.76

• 268.1

• 16.3

• 1279.35

The American Red Cross says that about 11% of the U.S. population has Type B blood. A blood drive is being held at your school. How many blood donors should the American Red Cross expect to collect from until it gets a donor with Type B blood?

• 9.1 donors

• 8.5 donors

• 10.3 donors

• Cannot be determined.

The American Red Cross says that about 11% of the U.S. population has Type B blood. A blood drive is being held at your school. What is the probability that the tenth blood donor is the first donor with Type B blood?

• approximately 0.00

• 0.316

• 0.0385 

• 0.279

Which of the following is true about geometric distributions?

• Geometric distributions are approximately skewed right.

• Geometric distributions are approximately symmetric.

• Geometric distributions are approximately skewed left.

• The shape could be symmetric or skewed.

Which of the following is false about binomial probabilities?

• Their distributions are approximately symmetric.

• Trials must be fixed.

• Events musts be independent.

• The probability of success must be 0.50

A test consists of 10 multiple choice questions with five choices for each question.  As an experiment, you GUESS on each and every answer without even reading the questions. 
What is the probability of getting exactly 6 questions correct on this test?

• 0.6%

• 0.00001%

• 0.0064%

• 0.0002%

When rolling a fair die 100 times, what is the probability of rolling a "4"exactly 25 times?

• 0.010

• 0.167

• 0.25

• 0.021

Which one of these variables is a continuous random variable?

• The time it takes a randomly selected student to complete an exam.

• The number of tattoos a randomly selected person has.

• The number of women taller than 68 inches in a random sample of 5 women. 

• The number of correct guesses on a multiple choice test. 

The owner of a pet store is trying to decide whether to discontinue selling specialty clothes for pets. She suspects that only 4% of the customers buy those clothes. The owner had 275 customers that day. Assuming this was a typical day, what is the mean and standard deviation of customers who buy specialty clothes?

• 11 customers, give or take 3.25

• 25 customers, give or take 24.5

• 11 customers, give or take 3.32

• Not enough information.

Which one of these variables is a binomial random variable?

• Time it takes a randomly selected student to complete a multiple choice exam

• Number of textbooks a randomly selected student bought this term 

• Number of women taller than 68 inches in a random sample of 5 women

• Number of CDs a randomly selected person owns