Introduction to Normal Distribution

​It is symmetric with respect to the mean or middle.

The mean is always at the center of the normal distribution curve. We use the Greek letter "μ" to denote this number. It is called mu, and you pronounce it "m-you"

We add and subtract standard deviations from the mean. We use the Greek letter "σ" to denote this number. It is called sigma, and you pronounce it just like it looks. In the graph to the right, two standard deviations below the average would be the number 25, and we would call this μ-2σ.

68% of the data lies within ± one standard deviation

95% of the data lies within ± two standard deviations

99.7% of the data lies within ± three standard deviations