7.2 Review questions

$X$ ~

• A

  $U(\mathrm{0,4})$

• B

  $U(\text{10},2)$

• C

  $\text{Exp}(2)$

• D

  $N(\mathrm{2,1})$

The average wait time is:

• A

  1 hour

• B

  2 hour

• C

  2.5 hour

• D

  4 hour

Suppose that it is now past noon on a delivery day. The probability that a person must wait at least $1\frac{1}{2}$ more hours is:

• A

  $\frac{1}{4}$

• B

  $\frac{1}{2}$

• C

  $\frac{3}{4}$

• D

  $\frac{3}{8}$

Given: $X\text{~}\text{Exp}(\frac{1}{3})$ .

• A

  Find $P(X>1)$

• B

  Calculate the minimum value for the upper quartile.

• C

  Find $P(X=\frac{1}{3})$

• 40% of full-time students took 4 years to graduate
• 30% of full-time students took 5 years to graduate
• 20% of full-time students took 6 years to graduate
• 10% of full-time students took 7 years to graduate

The expected time for full-time students to graduate is:

• A

  4 years

• B

  4.5 years

• C

  5 years

• D

  5.5 years

Which of the following distributions is described by the following example?

Many people can run a short distance of under 2 miles, but as the distance increases, fewer people can run that far.

• A

  Binomial

• B

  Uniform

• C

  Exponential

• D

  Normal

The length of time to brush one’s teeth is generally thought to be exponentially distributed with a mean of $\frac{3}{4}$ minutes. Find the probability that a randomly selected person brushes his/her teeth less than $\frac{3}{4}$ minutes.

• A

  0.5

• B

  $\frac{3}{4}$

• C

  0.43

• D

  0.63

Which distribution accurately describes the following situation?

A 2008 report on technology use states that approximately 20 percent of U.S. households have never sent an e-mail. (source: http://www.webguild.org/2008/05/20-percent-of-americans-have-never-used-email.php) Suppose that we select a random sample of fourteen U.S. households .

$X=$ the number of households in the sample of 14 households that have never sent an email

• A

  $B(\text{14},0\text{.}\text{20})$

• B

  $P(2\text{.}8)$

• C

  $N(2\text{.}\mathrm{8,2}\text{.}\text{24})$

• D

  $\text{Exp}(\frac{1}{0\text{.}\text{20}})$