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Ch. 5 - Normal Probability Distributions
Larson - Elementary Statistics: Picturing the World 8th Edition
Larson8th EditionElementary Statistics: Picturing the WorldISBN: 9780137493470Not the one you use?Change textbook
Chapter 5, Problem 5.1.38a

[APPLET] Milk Consumption You are performing a study about weekly per capita milk consumption. A previous study found weekly per capita milk consumption to be normally distributed, with a mean of 48.7 fluid ounces and a standard deviation of 8.6 fluid ounces. You randomly sample 30 people and record the weekly milk consumptions shown below.
Data table displaying weekly milk consumption values for a sample of 30 individuals, ranging from 25 to 65 fluid ounces.
a. Draw a frequency histogram to display these data. Use seven classes. Do the consumptions appear to be normally distributed? Explain.

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Step 1: Organize the data into a frequency table. First, determine the range of the data by subtracting the smallest value (25) from the largest value (65). Divide this range into seven equal intervals (classes). Each interval should have the same width, calculated as (Range / Number of Classes).
Step 2: Count the number of data points that fall into each interval (class). This will give you the frequency for each class. For example, if the first interval is 25-34, count how many values in the dataset fall within this range.
Step 3: Draw the frequency histogram. On the x-axis, label the intervals (classes). On the y-axis, label the frequency (number of occurrences). For each interval, draw a bar whose height corresponds to the frequency of that interval.
Step 4: Analyze the shape of the histogram. Check whether the data appears to follow a bell-shaped curve, which is characteristic of a normal distribution. Look for symmetry and a peak near the mean (48.7 fluid ounces).
Step 5: Compare the histogram to the properties of a normal distribution. If the histogram is roughly symmetric and bell-shaped, the data can be considered approximately normally distributed. If there are significant skewness or multiple peaks, the data may not be normally distributed.

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Key Concepts

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

Normal Distribution

Normal distribution is a probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean. It is characterized by its bell-shaped curve, defined by its mean and standard deviation. In this context, understanding normal distribution is crucial for analyzing the milk consumption data and determining if it follows this pattern.
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Histogram

A histogram is a graphical representation of the distribution of numerical data, where the data is divided into intervals (or bins) and the frequency of data points in each interval is represented by the height of the bars. Creating a histogram for the milk consumption data will help visualize the distribution and assess its shape, which is essential for determining if the data appears normally distributed.
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Intro to Histograms

Sampling Distribution

The sampling distribution refers to the probability distribution of a statistic (like the sample mean) obtained from a large number of samples drawn from a specific population. In this case, understanding the sampling distribution is important because it allows us to make inferences about the population mean of milk consumption based on the sample of 30 individuals, especially in relation to the known mean and standard deviation.
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Related Practice
Textbook Question

Approximating Binomial Probabilities In Exercises 19–26, determine whether you can use a normal distribution to approximate the binomial distribution. If you can, use the normal distribution to approximate the indicated probabilities and sketch their graphs. If you cannot, explain why and use a binomial distribution to find the indicated probabilities. Identify any unusual events. Explain.


Advancing Research In a survey of U.S. adults, 77% said are willing to share their personal health information to advance medical research. You randomly select 500 U.S. adults. Find the probability that the number who are willing to share their personal health information to advance medical research is (a) at most 400

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Textbook Question

Ice Cream The weights of ice cream cartons are normally distributed with a mean weight of 10 ounces and a standard deviation of 0.5 ounce.


a. What is the probability that a randomly selected carton has a weight greater than 10.21 ounces?


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Textbook Question

Pregnancy Length Use the normal distribution in Exercise 15.


a. What percent of the new mothers had a pregnancy length of less than 290 days?

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Textbook Question

Finding Specified Data Values In Exercises 31–38, answer the questions about the specified normal distribution.


Red Blood Cell Count The red blood cell counts (in millions of cells per microliter) for a population of adult males can be approximated by a normal distribution, with a mean of 5.4 million cells per microliter and a standard deviation of 0.4 million cells per microliter.


a. What is the minimum red blood cell count that can be in the top 25% of counts?


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Textbook Question

Uniform Distribution A uniform distribution is a continuous probability distribution for a random variable x between two values a and b (a<b), where (a ≤ x ≤ b) and all of the values of x are equally likely to occur. The graph of a uniform distribution is shown below.

The probability density function of a uniform distribution is


on the interval from (x=a) to (x=b). For any value of x less than a or greater than b, y=0 . In Exercises 59 and 60, use this information.


For two values c and d, where a ≤ c < d ≤ b, the probability that x lies between c and d is equal to the area under the curve between c and d, as shown below.



So, the area of the red region equals the probability that x lies between c and d. For a uniform distribution from (a=1) to (b=25) , find the probability that


a. x lies between 2 and 8.

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Textbook Question

Approximating Binomial Probabilities In Exercises 19–26, determine whether you can use a normal distribution to approximate the binomial distribution. If you can, use the normal distribution to approximate the indicated probabilities and sketch their graphs. If you cannot, explain why and use a binomial distribution to find the indicated probabilities. Identify any unusual events. Explain.


Athletes on Social Issues In a survey of college athletes, 84% said they are willing to speak up and be more active in social issues. You randomly select 25 college athletes. Find the probability that the number who are willing to speak up and be more active in social issues is (a) at least 24

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