BStat Exam 2

The time to complete the construction of a soapbox derby car is normally distributed with a mean of three hours and a standard deviation of one hour. Find the probability that it would take exactly 3.7 hours to construct a soapbox derby car.

0.0000

Consider the following cumulative distribution function for the discrete random variable X. X: 1 2 3 4 P( X < x): .3 .44 .72 1.00 What is the probability that X equals 2?

0.14

Alex is in a hurry to get to work and is rushing to catch the bus. She knows that the bus arrives every six minutes during rush hour, but does not know the exact times the bus is due. She realizes that from the time she arrives at the stop, the amount of time that she will have to wait follows a uniform distribution with a lower bound of 0 minutes and an upper bound of six minutes. What is the probability that she will have to wait less than two minutes?

0.3333

The probability that a normal random variable is less than its mean is

0.5

On a particular production line, the likelihood that a light bulb is defective is 5%. Ten light bulbs are randomly selected. What are the mean and variance of the number of defective light bulbs?

0.50 and 0.475

Number Sold: 0 1 2 Probability: .2 .4 .4 What is the standard deviation of the number of homes sold by the realtor during a month?

0.75

For a particular clothing store, a marketing firm finds that 16% of $10-off coupons delivered by mail are redeemed. Suppose six customers are randomly selected and are mailed $10-off coupons. What is the expected number of coupons that will be redeemed?

0.96

What are two key properties of a discrete probability distribution?

0≤P (X = x) ≤1 and ∑P (X = xi ) = 1

Number Sold: 0 1 2 Probability: .2 .4 .4 What is the expected number of homes sold by the realtor during a month?

1.2

According to geologists, the San Francisco Bay Area experiences five earthquakes with a magnitude of 6.5 or greater every 100 years. What is the standard deviation of the number of earthquakes with a magnitude of 6.5 or greater striking the San Francisco Bay Area in the next 40 years?

1.414

According to a Department of Labor report, the city of Detroit had a 20% unemployment rate in May. Eight working-age residents were chosen at random. What was the expected number of unemployed residents, when eight working-age residents were randomly selected?

1.6

Xi: 0 1 2 3 P( X= xi): .1 .2 .4 .3 The expected value is

1.90

The height of the probability density function f(x) of the uniform distribution defined on the interval [a, b] is ______.

1/(b − a) between a and b, and zero otherwise

How many parameters are needed to fully describe any normal distribution?

2- the mean and the standard deviation

According to geologists, the San Francisco Bay Area experiences five earthquakes with a magnitude of 6.5 or greater every 100 years. What is the expected value of the number of earthquakes with a magnitude of 6.5 or greater striking the San Francisco Bay Area in the next 40 years?

2000

A daily mail is delivered to your house between 1:00 p.m. and 5:00 p.m. Assume delivery times follow the continuous uniform distribution. Determine the percentage of mail deliveries that are made after 4:00 p.m.

25%

According to a study by the Centers for Disease Control and Prevention, about 33% of U.S. births are Caesarean deliveries. Suppose seven expectant mothers are randomly selected. The expected number of mothers who will not have a Caesarean delivery is

4.69

Sarah's portfolio has an expected annual return at 8%, with an annual standard deviation at 12%. If her investment returns are normally distributed, then in any given year Sarah has an approximate ______.

50% chance that the actual return will be greater than 8%

You work in marketing for a company that produces work boots. Quality control has sent you a memo detailing the length of time before the boots wear out under heavy use. They find that the boots wear out in an average of 208 days, but the exact amount of time varies, following a normal distribution with a standard deviation of 14 days. For an upcoming ad campaign, you need to know the percent of the pairs that last longer than six months—that is, 180 days. Use the empirical rule to approximate this percent.

97.5%

A consumer who is risk averse is best characterized as

A consumer who demands a positive expected gain as compensation for taking risk.

How would vou characterize a consumer who is risk loving?

A consumer who may accept a risky prospect even if the expected gain is negative.

Which of the following is correct?

A continuous random variable has a probability density function, and a discrete random variable has a probability mass function.

Which of the following statements is the most accurate about a binomial random variable?

It counts the number of successes in a given number of trials.

Which of the following statements is the most accurate about a Poison random variable?

It counts the number of successes in a specified time or space interval

The cumulative distribution function F (x) of a continuous random variable X with the probability density function F (x) is which of the following?

The area under f over all values that are x or less.

Which of the following does not represent a continuous random variable?

The number of customer arrivals to a bank between 10 am and 11 am.

Which of the following is best described as a Poisson variable?

The number of positive reviews in a week.

Which of the following is FALSE about a continuous random variable?

The probability that its value is within a specific interval is equal to one

Which of the following is an example of a uniformly distributed random variable?

The scheduled arrival time of a cable technician.

What does it mean when we say that the tails of the normal curve are asymptotic to the x axis?

The tails get closer and closer to the x axis but never touch it.

A consumer who is risk neutral is best characterized as

a consumer who completely ignores risk and makes his or her decisions based solely on expected values

Which of the following is not a characteristic of a probability density function f(x)?

f(x) is symmetric around the mean.

A continuous random variable has the uniform distribution on the interval [a, b] if its probability density function f(x)

is constant for all x between a and b, and 0 otherwise

We can think of the expected value of a random variable X as

the long-run average of the random variables generated over infinitely many independent repetitions