Category Archives: Normal Distributions

The Middle 80% Is Not 80th Percentile

A student sent me an email about a practice problem involving finding the middle 80% of a normal distribution. The student was confusing the middle 80% of a bell curve with the 80th percentile. The student then tried to answer … Continue reading

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Comparing Growth Charts

Suppose both an 8-year old boy and a 10-year old boy are 54 inches tall (four feet six inches). Physically they are of the same heights. But a better way to compare is to find out where each boy stands … Continue reading

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An Example of a Normal Curve

One way to estimate probabilities is to use empirical data. However, if the histogram of the data shapes like a bell curve (or reasonably close to a bell curve), we can use a normal curve to estimate probabilities. All we … Continue reading

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A Student’s View of the Normal Distribution

In my teaching, I always strive to encourage students to look at statistics from a practical point of view. In a recent class period covering the normal distribution, I indicated that data values more than 3 standard deviations away from … Continue reading

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