Rule
1 SD from the mean: 68% of the total area
2 SD from the mean: 95% of the total area
3 SD from the mean: 99% of the total area
The entire curve is 100%
So half of the curve(slide in the middle) is 50%
Alternate Section Area
Example 10<x<20
We know 20-80 is 99.7%, then 100-99.7% = 0.03, thats the area from 10-20 and 80-90. then, its divided by 2 so 0.015
Example 50-80
99.7 divided by 2 = 49.85