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 P 10, which is the IQ score separating the bottom 10% from the top 90%.

The IQ score that separates the bottom 10% from the top 90% is Upper P 10 equals______?

Solution

First, we get the z score from the given left tailed area. As          
          
Left tailed area =    0.1      
          
Then, using table or technology,          
          
z =    -1.281551566      
          
As x = u + z * s / sqrt(n)          
          
where          
          
u = mean =    105      
z = the critical z score =    -1.281551566      
s = standard deviation =    15      
          
Then          
          
x = critical value =    85.77672652   [ANSWER]