Assume that adults have IQ scores that are normally distribu

Assume that adults have IQ scores that are normally distributed with a mean of

105

and a standard deviation

15.

Find

Upper P9,

which is the IQ score separating the bottom

9%

from the top

91%

Solution

First, we get the z score from the given left tailed area. As          
          
Left tailed area =    0.09      
          
Then, using table or technology,          
          
z =    -1.340755034      
          
As x = u + z * s,          
          
where          
          
u = mean =    105      
z = the critical z score =    -1.340755034      
s = standard deviation =    15      
          
Then          
          
x = P9 =    84.88867449   [ANSWER]