### 5.1 Continuous Probability Functions

Which type of distribution does the graph illustrate?

What does the shaded area represent? *P*(___< *x* < ___)

For a continuous probablity distribution, 0 ≤ *x* ≤ 15. What is *P*(*x* > 15)?

For a continuous probability distribution, 0 ≤ *x* ≤ 10. What is *P*(*x* = 7)?

A **continuous** probability function is restricted to the portion between *x* = 0 and 7. What is *P*(*x* = 10)?

*f*(*x*) for a continuous probability function is $\frac{1}{5}$, and the function is restricted to 0 ≤ *x* ≤ 5. What is *P*(*x* < 0)?

*f*(*x*), a continuous probability function, is equal to $\frac{1}{12}$, and the function is restricted to 0 ≤ *x* ≤ 12. What is *P* (0 < *x* < 12)?

Find the probability that *x* falls in the shaded area.

Find the probability that *x* falls in the shaded area.

*f*(*x*), a continuous probability function, is equal to $\frac{1}{3}$ and the function is restricted to 1 ≤ *x* ≤ 4. Describe $P\left(x>\frac{3}{2}\right).$

### 5.2 The Uniform Distribution

*Use the following information to answer the next 10 questions.* The data that follow are the square footage (in 1,000 feet squared) of 28 homes:

1.5 | 2.4 | 3.6 | 2.6 | 1.6 | 2.4 | 2.0 |

3.5 | 2.5 | 1.8 | 2.4 | 2.5 | 3.5 | 4.0 |

2.6 | 1.6 | 2.2 | 1.8 | 3.8 | 2.5 | 1.5 |

2.8 | 1.8 | 4.5 | 1.9 | 1.9 | 3.1 | 1.6 |

The sample mean = 2.50 and the sample standard deviation = 0.8302.

The distribution can be written as *X* ~ *U*(1.5, 4.5).

What type of distribution is this?

What is the height of *f*(*x*) for the continuous probability distribution?

Graph *P*(2 < *x* < 3).

What is *P*(x < 3.5| *x* < 4)?

What is the 90^{th} percentile of square footage for homes?

Find the probability that a randomly selected home has more than 3,000 square feet given that you already know the house has more than 2,000 square feet.

*Use the following information to answer the next eight exercises.* A distribution is given as *X* ~ *U*(0, 12).

What is *a*? What does it represent?

What is the probability density function?

What is the theoretical standard deviation?

Find *P*(*x* > 9).

*Use the following information to answer the next 12 exercises.* The age of cars in the staff parking lot of a suburban college is uniformly distributed from six months (0.5 years) to 9.5 years.

What is being measured here?

Are the data discrete or continuous?

The distribution for *X* is ______.

Graph the probability distribution.

- Sketch the graph of the probability distribution.
- Identify the following values:
- Lowest value for $\overline{x}$: _______
- Highest value for $\overline{x}$: _______
- Height of the rectangle: _______
- Label for
*x*-axis (words): _______ - Label for
*y*-axis (words): _______

Find the probability that a randomly chosen car in the lot was less than four years old.

- Sketch the graph, and shade the area of interest.
- Find the probability.
*P*(*x*< 4) = _______

Considering only the cars less than 7.5 years old, find the probability that a randomly chosen car in the lot was less than four years old.

- Sketch the graph, shade the area of interest.
- Find the probability.
*P*(*x*< 4|*x*< 7.5) = _______

What has changed in the previous two problems that made the solutions different?

Find the third quartile of ages of cars in the lot. This means you will have to find the value such that $\frac{3}{4}$, or 75 percent, of the cars are at most (less than or equal to) that age.

- Sketch the graph, and shade the area of interest.
- Find the value
*k*such that*P*(*x*<*k*) = 0.75. - The third quartile is _______

### 5.3 The Exponential Distribution (Optional)

*Use the following information to answer the next 10 exercises.* A customer service representative must spend different amounts of time with each customer to resolve various concerns. The amount of time spent with each customer can be modeled by the following distribution: *X* ~ *Exp*(0.2)

What type of distribution is this?

What is *m*? What does it represent?

What is the standard deviation?

Graph the distribution.

Find *P*(*x* > 6).

*Use the following information to answer the next eight exercises.* A distribution is given as *X* ~ *Exp*(0.75).

What is *m*?

What is the cumulative distribution function?

Find *P*(*x* < 4).

Find the median.

*Use the following information to answer the next eight exercises.* Carbon-14 is a radioactive element with a half-life of about 5,730 years. Carbon-14 is said to decay exponentially. The decay rate is 0.000121. We start with one gram of carbon-14. We are interested in the time (years) it takes to decay carbon-14.

What is being measured here?

In words, define the random variable *X*.

The distribution for *X* is ______.

Find the amount (percent of one gram) of carbon-14 lasting less than 5,730 years. The question means that you need to find *P*(*x* < 5,730).

- Sketch the graph, and shade the area of interest.
- Find the probability.
*P*(*x*< 5,730) = __________

Find the percentage of carbon-14 lasting longer than 10,000 years.

- Sketch the graph, and shade the area of interest.
- Find the probability.
*P*(*x*> 10,000) = ________

Thirty percent of carbon-14 will decay within how many years?

- Sketch the graph, and shade the area of interest.
- Find the value
*k*such that*P*(*x*<*k*) = 0.30.