If a normally distributed group of test scores have a mean o

If a normally distributed group of test scores have a mean of 80 and a standard deviation of 15, find the proportion of scores that will fall below 75. Round your answer to 2 decimal places.

Solution

Normal Distribution
Mean ( u ) =80
Standard Deviation ( sd )=15
Normal Distribution = Z= X- u / sd ~ N(0,1)                  
P(X < 75) = (75-80)/15
= -5/15= -0.3333
= P ( Z <-0.3333) From Standard Normal Table
= 0.3694