Hi,
Important to Understand z -values as they relate to the Standard Normal curve:
Below: z = 0, z = ± 1, z= ±2 , z= ±3 are plotted.
Note: z = 0 (x value the mean) 50% of the area under the curve is to the left and %50 to the right
For the normal distribution:
one standard deviation from the mean accounts for about 68.2% of the set
two standard deviations from the mean account for about 95.4%
and three standard deviations from the mean account for about 99.7%.
a normal distribution that has a mean of 100 and a standard deviation of 8.
p(92 < x < 108)= .682
p(84 < x < 116) = .954
p(x < 84) = (1-.954)/2