Using the 68-95-99.7 Rule

Use the distribution of male adult heights (I have a chart to refer to) to find the percentage of men in North America with heights
a) between 66 inches and 74 inches.
b) between 70 inches and 74 inches.
c) above 78 inches.

The solution: The 68-95-99.7 Rule states that approximately 68% of the data items fall within 1 standard deviation, 4, of the mean, 70.

mean - 1*standard deviation = 70-1*4=70-4=66
mean + 1*standard deviation = 70+1*4=70+4=74

Where did the 4 come from and how did they get it?

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wjm11 said:

In this problem it is given to you, so you do not yet need to know how it is calculated. It is good, however, that you are interested enough to ask. There is a formula used to find the Standard Deviation. The formula and example may be found here (and many other places):

http://en.wikipedia.org/wiki/Standard_deviation

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