/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 14 Use the data in the table below ... [FREE SOLUTION] | 91Ó°ÊÓ

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Use the data in the table below for sitting adult males and females (based on anthropometric survey data from Gordon, Churchill, et al.). These data are used often in the design of different seats, including aircraft seats, train seats, theater seats, and classroom seats. (Hint: Draw a graph in each case.) $$\begin{array}{|l|l|l|l|} \hline & \text { Mean } & \text { St. Dev. } & \text { Distribution } \\ \hline \text { Males } & 23.5 \mathrm{in} . & 1.1 \mathrm{in} . & \text { Normal } \\ \hline \text { Females } & 22.7 \mathrm{in} . & 1.0 \mathrm{in} . & \text { Normal } \\ \hline \end{array}$$ Find the probability that a female has a back-to-knee length greater than 24.0 in.

Short Answer

Expert verified
P(X > 24.0) = 0.0968

Step by step solution

01

- Understand the Problem

To find the probability that a female has a back-to-knee length greater than 24.0 inches, we need to use the normal distribution of the given data and perform a standard normal transformation.
02

- Identify Given Values

From the table, we know that the mean back-to-knee length for females is 22.7 inches, and the standard deviation is 1.0 inches. The length we are interested in is 24.0 inches.
03

- Standard Normal Transformation

We need to convert 24.0 inches to a z-score using the formula: $$z = \frac{x - \text{mean}}{\text{standard deviation}}$$ Substitute the values: $$z = \frac{24.0 - 22.7}{1.0} = 1.3$$
04

- Use Z-Table to Find Probability

Use the z-table to find the probability corresponding to a z-score of 1.3. The z-table gives the area to the left of the z-score. For a z-score of 1.3, the table value is 0.9032.
05

- Calculate the Desired Probability

We want the probability that the length is greater than 24.0 inches, which is the area to the right of the z-score. Subtract the z-table value from 1: $$P(X > 24.0) = 1 - P(Z < 1.3)$$ $$P(X > 24.0) = 1 - 0.9032 = 0.0968$$

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Key Concepts

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

z-score calculation
To understand the normal distribution probability, we must delve into z-score calculation first. The z-score, also known as the standard score, measures how many standard deviations an element is from the mean. This process helps us understand where a specific observation lies within a normal distribution.

The formula for calculating a z-score is simple: \(z = \frac{x - \text{mean}}{\text{standard deviation}}\).
Here, \(x\) is the value you want to convert, the \(\text{mean}\) is the average of the dataset, and \(\text{standard deviation}\) measures the dispersion of the dataset.
For instance, if the mean height of females is 22.7 inches with a standard deviation of 1.0 inch, and you want to find the z-score for a height of 24.0 inches, you substitute these values into the formula: \(z = \frac{24.0 - 22.7}{1.0} = 1.3\).
This means the height of 24.0 inches is \(1.3\) standard deviations above the mean.
standard normal transformation
Standard normal transformation is a vital concept when dealing with normal distribution probabilities. It usually involves converting a normal distribution to a standard normal distribution where the mean is zero and the standard deviation is one. This process is often termed 'standardizing'.

By transforming the data to the standard normal distribution, we make use of the z-table (or standard normal table) efficiently. As demonstrated in the original exercise, we transform an observed value \(24.0\) to a z-score \(1.3\). The transformed value is easier to work with for finding exact probabilities and comparing different datasets.

The formula to achieve this conversion is again: \(z = \frac{x - \text{mean}}{\text{standard deviation}}\).
This transformation aligns the data on a common scale, allowing seamless extrapolation of probabilities from the z-table. Remember, this transformation simplifies the pursuit of probability metrics across varied distributions.
probability finding using z-table
Once we calculate the z-score, the next step is to find the corresponding probability using the z-table. A z-table helps us work with the standard normal distribution and find the area (probability) to the left of any given z-score.

For example, from our previous calculation, the z-score of 1.3 corresponds to a probability of \(0.9032\). This value represents the probability that a randomly selected female will have a back-to-knee length less than 24.0 inches.
To find the probability of a value being greater than a specific z-score, we subtract this value from 1:

\(P(X > 24.0) = 1 - P(Z < 1.3)\)
\(P(X > 24.0) = 1 - 0.9032 = 0.0968\).
Therefore, there's about a \(9.68\)% chance that a randomly selected female will have a back-to-knee length greater than 24.0 inches. Working with the z-table empowers us to derive meaningful probabilities with straightforward arithmetic, making data insights more accessible.

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Most popular questions from this chapter

Constructing Normal Quantile Plots.Use the given data values to identify the corresponding z scores that are used for a normal quantile plot, then identify the coordinates of each point in the normal quantile plot. Construct the normal quantile plot, then determine whether the data appear to be from a population with a normal distribution. Female Arm Circumferences A sample of arm circumferences (cm) of females from Data Set 1 "Body Data" in Appendix \(B: 40.7,44.3,34.2,32.5,38.5 .\)

Normal Quantile Plot Data Set 1 "Body Data" in Appendix \(B\) includes the heights of 147 randomly selected women, and heights of women are normally distributed. If you were to construct a histogram of the 147 heights of women in Data Set \(1,\) what shape do you expect the histogram to have? If you were to construct a normal quantile plot of those same heights, what pattern would you expect to see in the graph?

When women were finally allowed to become pilots of fighter jets, engineers needed to redesign the ejection seats because they had been originally designed for men only. The ACES-II ejection seats were designed for men weighing between 140 lb and 211 lb. Weights of women are now normally distributed with a mean of 171 lb and a standard deviation of 46 lb (based on Data Set 1 "Body Data" in Appendix B). a. If I woman is randomly selected, find the probability that her weight is between 140 lb and 211 lb. b. If 25 different women are randomly selected, find the probability that their mean weight is between 140 lb and 211 lb. c. When redesigning the fighter jet ejection seats to better accommodate women, which probability is more relevant: the result from part (a) or the result from part (b)? Why?

Use these parameters (based on Data Set 1 "Body Data" in Appendix \(B\) ): Men's heights are normally distributed with mean 68.6 in. and standard deviation 2.8 in. Women's heights are normally distributed with mean 63.7 in. and standard deviation 2.9 in. Air Force Pilots The U.S. Air Force requires that pilots have heights between 64 in. and 77 in. a. Find the percentage of men meeting the height requirement. b. If the Air Force height requirements are changed to exclude only the tallest \(2.5 \%\) of men and the shortest \(2.5 \%\) of men, what are the new height requirements?

Find the indicated area under the curve of the standard normal distribution; then convert it to a percentage and fill in the blank. The results form the basis for the range rule of thumb and the empirical rule introduced in Section 3-2. About _____ \(\%\) of the area is between \(z=-3\) and \(z=3\) (or within 3 standard deviations of the mean).

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