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Ch. 2 - Descriptive Statistics
Larson - Elementary Statistics: Picturing the World 8th Edition
Larson8th EditionElementary Statistics: Picturing the WorldISBN: 9780137493470Not the one you use?Change textbook
All textbooksLarson 8th EditionCh. 2 - Descriptive StatisticsProblem 2.T.8b
Chapter 2, Problem 2.T.8b

The mean gestational length of a sample of 208 horses is 343.7 days, with a standard deviation of 10.4 days. The data set has a bell-shaped distribution.


b. Determine whether a gestational length of 318.4 days is unusual.

Verified step by step guidance
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Step 1: Understand the concept of 'unusual' values in a bell-shaped distribution. In statistics, a value is considered unusual if it lies more than 2 standard deviations away from the mean.
Step 2: Calculate the lower and upper bounds for usual values using the formula: Lower Bound = Mean - 2 × Standard Deviation, and Upper Bound = Mean + 2 × Standard Deviation. Use the given mean (343.7 days) and standard deviation (10.4 days) in the formula.
Step 3: Substitute the values into the formula for the lower bound: Lower Bound = 343.7 - 2 × 10.4. Perform the subtraction and multiplication to find the lower bound.
Step 4: Substitute the values into the formula for the upper bound: Upper Bound = 343.7 + 2 × 10.4. Perform the addition and multiplication to find the upper bound.
Step 5: Compare the given gestational length of 318.4 days to the calculated lower and upper bounds. If 318.4 days lies outside these bounds, it is considered unusual; otherwise, it is not.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Mean

The mean is the average value of a data set, calculated by summing all the values and dividing by the number of observations. In this context, the mean gestational length of 343.7 days represents the central tendency of the sample of horses, providing a benchmark against which individual gestational lengths can be compared.
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Calculating the Mean

Standard Deviation

Standard deviation is a measure of the amount of variation or dispersion in a set of values. A low standard deviation indicates that the values tend to be close to the mean, while a high standard deviation indicates a wider spread. Here, the standard deviation of 10.4 days helps assess how typical or atypical a gestational length of 318.4 days is in relation to the mean.
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Z-Score

A Z-score quantifies how many standard deviations a data point is from the mean. It is calculated by subtracting the mean from the value and then dividing by the standard deviation. In this case, calculating the Z-score for a gestational length of 318.4 days will help determine if it is considered unusual, typically defined as a Z-score less than -2 or greater than 2.
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Related Practice
Textbook Question

The data set represents the number of movies that a sample of 20 people watched in a year.

121 148 94 142 170 88 221 106 18 67

149 28 60 101 134 168 92 154 53 66

b. Display the data using a frequency histogram and a frequency polygon on the same axes.

Textbook Question

Use the frequency histogram

a. to determine the number of classes.

Textbook Question

Use the frequency distribution in Exercise 4 to estimate the sample mean and sample standard deviation of the data. Do the formulas for grouped data give results that are as accurate as the individual entry formulas? Explain.

Textbook Question

The table lists the number of albums by The Beatles that received sales certifications. Display the data using (b) a Pareto chart. (Source: Recording Industry Association of America)

Textbook Question

Extending Concepts


Golf The distances (in yards) for nine holes of a golf course are listed.

336 393 408 522 147 504 177 375 360


a. Find the mean and the median of the data.

Textbook Question

What Would You Do? You work at a bank and are asked to recommend the amount of cash to put in an ATM each day. You do not want to put in too much (which would cause security concerns) or too little (which may create customer irritation). The daily withdrawals (in hundreds of dollars) for 30 days are listed. 72 84 61 76 104 76 86 92 80 88 98 76 97 82 84 67 70 81 82 89 74 73 86 81 85 78 82 80 91 83

Construct a relative frequency histogram for the data. Use 8 classes.

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