
This is XBar. It tells us the Average of a group of numbers (in this case average height). XBar is the middle of the curve where we have the largest percentage of men.
s = sigma = Standard Deviation
s is the Greek letter Sigma. It is the distance from the center of the curve to the point where the curve stops curving downward and starts curving outward. We�re interested in points at 1, 2 and 3 Standard Deviations from the Mean (the center).
If we measure 1 Standard Deviation on each side of the center of the curve , 68% of the Area will be between the lines drawn through these points.
The Human Proportions table tells us the Standard Deviation (s  dispersion) of men�s heights is 0.07 meters, so by simple addition and subtraction we know that 68% of the men are between 1.73 and 1.87 meters.
1.8 + 0.07 = 1.87
1.8  0.07 = 1.73
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