Question

Assume that adults have IQ scores that are normally distributed with a mean of 100.5 and a standard deviation 16. Find the first quartile Q₁, which is the IQ score separating the bottom 25% from the top 75%. (Hint: Draw a graph.) 

The first quartile is _______ 

Answer 1

Solution :

= 100.5

= 16

Using stnadard normal table ,

P(Z < z) = 0.25

P(Z < -0.6745) = 0.25

z = -0.6745

Using z-score formula ,

x = z* + = -0.6745 * 16 + 100.5 = 89.7

The first quartile is 89.7