# Math Help - Normal Distribution HELP!

1. ## Normal Distribution HELP!

Hello, I don't understand how the NORMAL DISTRIBUTION column of the attached chart is calculated, can someone please explain?

The mean is 40 and the Standard Deviation is 10

2. ## Re: Normal Distribution HELP!

20 is 2 standard deviations below the mean $\frac{20-40}{10}=-2$ and 30 is 1 standard deviations below the mean $\frac{30-40}{10}=-1$