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A uniform distribution is defined over the interval from 6 to 10. a. What are the values for \(a\) and \(b\) ? b. What is the mean of this uniform distribution? c. What is the standard deviation? d. Show that the total area is 1.00 . e. Find the probability of a value more than 7 . f. Find the probability of a value between 7 and \(9 .\)

Short Answer

Expert verified
a: 6, 10; b: 8; c: \( \frac{2\sqrt{3}}{3} \); d: Yes; e: \( \frac{3}{4} \); f: \( \frac{1}{2} \).

Step by step solution

01

Identify Parameters of the Uniform Distribution

For a uniform distribution defined over the interval from 6 to 10, the parameter \(a\) is the lower bound, and \(b\) is the upper bound. Thus, \(a = 6\) and \(b = 10\).
02

Calculate the Mean of the Uniform Distribution

The mean (or expected value) \( \mu \) of a uniform distribution is calculated using the formula \( \mu = \frac{a+b}{2} \). Substituting the values from the interval, \( \mu = \frac{6+10}{2} = 8 \).
03

Determine the Standard Deviation

The standard deviation \( \sigma \) for a uniform distribution is calculated by the formula \( \sigma = \frac{b-a}{\sqrt{12}} \). For the interval from 6 to 10, \( \sigma = \frac{10-6}{\sqrt{12}} = \frac{4}{\sqrt{12}} = \frac{4}{2\sqrt{3}} = \frac{2\sqrt{3}}{3} \approx 1.155 \).
04

Verify Total Probability Area

For a uniform distribution, the total area under the probability density function (PDF) should be 1. The height of the PDF for a uniform distribution is \( \frac{1}{b-a} \). Therefore, \( \frac{1}{10-6} = \frac{1}{4} \). The area of the rectangle is height multiplied by base, \( \frac{1}{4} \times (10 - 6) = 1 \). This confirms that the total area is 1.
05

Find Probability for a Value More Than 7

The probability of a value more than 7 is the area under the PDF from 7 to 10. The length of this interval is 10 - 7 = 3. Thus, Probability = \( \frac{1}{4} \times 3 = \frac{3}{4} \).
06

Calculate Probability Between 7 and 9

To find the probability of a value between 7 and 9, calculate the area under the PDF from 7 to 9. The length of this interval is 9 - 7 = 2, thus Probability = \( \frac{1}{4} \times 2 = \frac{1}{2} \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Mean of Uniform Distribution
The mean of a uniform distribution is essentially the average value we expect from this distribution. In the context of a uniform distribution, where every outcome is equally likely, the mean gives us a good estimate of the center of the distribution. This is calculated using a simple formula: \( \mu = \frac{a+b}{2} \). Here, \(a\) and \(b\) represent the lower and upper boundaries of the interval, respectively.

In our example, with the interval from 6 to 10, the mean would be \( \mu = \frac{6+10}{2} = 8 \). This value, 8, tells us that the center of our distribution is at 8, a balance point around which the distribution spans. It's important to remember that the mean for a uniform distribution is always midway between the lower and upper bounds.
Standard Deviation of Uniform Distribution
Standard deviation is a measure of how spread out the numbers in a distribution are. For a uniform distribution, it gives us an idea of how much the values deviate from the mean. The formula for the standard deviation of a uniform distribution is: \( \sigma = \frac{b-a}{\sqrt{12}} \).

Breaking this down, the difference \(b-a\) represents the span of the interval. Dividing by \(\sqrt{12}\) standardizes this measure, giving us a clearer picture of variability. In the case of our interval from 6 to 10, we calculate \( \sigma = \frac{10-6}{\sqrt{12}} = \frac{4}{\sqrt{12}} = \frac{2\sqrt{3}}{3} \approx 1.155 \).

This approximate value, 1.155, indicates how widely spread the values are around the mean. A higher standard deviation would mean more variability, while a lower value suggests that the numbers are more centered around the mean.
Probability Density Function
The probability density function (PDF) for a uniform distribution provides us with a constant probability for any specific interval within the distribution. For a uniform distribution, this function is represented by a rectangle, since the probability is constant for each interval.

The height of this rectangle, or the value of the PDF, is determined by \( \frac{1}{b-a} \). This is derived from the need for the total area under the PDF to equal 1. Hence, for our interval from 6 to 10, the height is \( \frac{1}{10-6} = \frac{1}{4} \).

This means that any sub-interval within 6 to 10 will have this consistent probability density. It's this uniformity that characterizes the uniform distribution, reflecting the equal likelihood of any outcome across the defined range.
Total Probability Area
In probability theory, a fundamental rule is that the total probability over all possible outcomes must equal 1. This rule is upheld in uniform distribution through the total area under the probability density function (PDF).

For our distribution between 6 and 10, the PDF forms a rectangle, with a height of \( \frac{1}{4} \) (as derived from \( \frac{1}{b-a} \)), and a base of \(10 - 6 = 4\). The area of this rectangle is height multiplied by the base, resulting in \( \frac{1}{4} \times 4 = 1 \).

Thus, the total probability area is confirmed to be 1, satisfying the principle of total probability. This effectively assures us that all possible outcomes of the distribution (any number between 6 and 10) are accounted for within this model.

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Most popular questions from this chapter

In economic theory, a "hurdle rate" is the minimum return that a person requires before he or she will make an investment. A research report says that annual returns from a specific class of common equities are distributed according to a normal distribution with a mean of \(12 \%\) and a standard deviation of \(18 \%\). A stock screener would like to identify a hurdle rate such that only 1 in 20 equities is above that value Where should the hurdle rate be set?

The mean of a normal probability distribution is \(500 ;\) the standard deviation is \(10 .\) a. About \(68 \%\) of the observations lie between what two values? b. About \(95 \%\) of the observations lie between what two values? c. Practically all of the observations lie between what two values?

A recent article in the Cincinnati Enquirer reported that the mean labor cost to repair a heat pump is \(\$ 90\) with a standard deviation of \(\$ 22 .\) Monte's Plumbing and Heating Service completed repairs on two heat pumps this morning. The labor cost for the first was \(\$ 75,\) and it was \(\$ 100\) for the second. Assume the distribution of labor costs follows the normal probability distribution. Compute \(z\) values for each, and comment on your findings.

A normal population has a mean of 80.0 and a standard deviation of \(14.0 .\) a. Compute the probability of a value between 75.0 and 90.0 . b. Compute the probability of a value of 75.0 or less. c. Compute the probability of a value between 55.0 and 70.0 .

The price of shares of Bank of Florida at the end of trading each day for the last year followed the normal distribution. Assume there were 240 trading days in the year. The mean price was \(\$ 42.00\) per share and the standard deviation was \(\$ 2.25\) per share. a. What is the probability that the end-of-day trading price is over \(\$ 45.00 ?\) Estimate the number of days in a year when the trading price finished above \(\$ 45.00 .\) b. What percent of the days was the price between \(\$ 38.00\) and \(\$ 40.00 ?\) c. What is the minimum share price for the top \(15 \%\) of end-of-day trading prices?

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