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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.RE.8

In Exercises 7–18, find the indicated area under the standard normal curve. If convenient, use technology to find the area.


To the left of z = -1.95

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Step 1: Understand the problem. You are tasked with finding the area under the standard normal curve to the left of z = -1.95. This represents the cumulative probability for a z-score of -1.95 in a standard normal distribution.
Step 2: Recall that the standard normal distribution is symmetric about the mean (z = 0), and the total area under the curve is 1. The area to the left of a given z-score represents the cumulative probability up to that z-score.
Step 3: Use the z-score table (also called the standard normal table) or technology (such as a graphing calculator or statistical software) to find the cumulative probability corresponding to z = -1.95. The table or software will provide the area to the left of this z-score.
Step 4: If using a z-score table, locate the row corresponding to -1.9 and the column corresponding to 0.05 (since -1.95 = -1.9 + 0.05). The intersection of this row and column gives the cumulative probability.
Step 5: If using technology, input the z-score of -1.95 into the appropriate function (e.g., 'normalcdf' on a calculator or a similar function in statistical software) to directly obtain the cumulative probability. This value represents the area under the curve to the left of z = -1.95.

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Key Concepts

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

Standard Normal Distribution

The standard normal distribution is a special normal distribution with a mean of 0 and a standard deviation of 1. It is used to describe how data points are distributed in a standardized way, allowing for comparison across different datasets. The area under the curve represents probabilities, with the total area equaling 1.
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Z-scores

A Z-score indicates how many standard deviations a data point is from the mean of a distribution. It is calculated by subtracting the mean from the data point and dividing by the standard deviation. In the context of the standard normal distribution, a Z-score of -1.95 means the value is 1.95 standard deviations below the mean.
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Area Under the Curve

The area under the curve of a probability distribution represents the likelihood of a random variable falling within a particular range. For the standard normal distribution, this area can be found using Z-tables or technology, such as statistical software, to determine probabilities associated with specific Z-scores.
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