Posted by Lyndon on .
For a normal distribution with a mean of m = 80 and a standard deviation of s = 20, find the proportion of the population corresponding to each of the following scores.
a. Scores greater than 85
b. Scores less than 100
c. Scores between 70 and 90
I believe this is the correct formula to start with but am unclear on how to finish it. Any help would be appreciated.
a. z = Xm= 85–80 = 5 = 0.25
s 20 20
b. z = Xm= 100–80 = 20 = 1.00
s 20 20
c. z = Xm= 70–80 = 10 = 0.25
s 20 20
z = Xm= 90–80 = 10 = 0.50
s 20 20

Statistics 
PsyDAG,
What does "s 20 20" mean?
Z = (xmean)/SD
Type equation completely to avoid mistakes.
c. 10/20 = ?
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportions related to the Z scores you have found.
I hope this helps.