Question

Assume that adults have IQ scores that are normally distributed with a mean of 103.9 and a standard deviation 24.9. Find the first quartile Upper Q 1​, which is the IQ score separating the bottom​ 25% from the top​ 75%. (Hint: Draw a​ graph.) The first quartile

Answer 1

SOLUTION:

Given that,

mean =  = 103.9

standard deviation =  = 24.9

Using standard normal table,

P(Z < z) = 25%

=(Z < z) = 0.25  

= P(Z < z ) = 0.25  

z = -0.67   

Using z-score formula  

x = z +

x = -0.67 *24.9+103.9

x = 87.217

  = 103.9