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 P10, which is the IQ score separating the bottom 10% from the top 90%.

Solution

Answer to the question)
We got

M = 105

s = 15

P(x< x) = 0.90

the area to the left 0.90 corresponds to z = 1.28

.

Thus we can make use of the z formula

z = (x - M) / s

1.28 = (x - 105) / 15

1.28 * 15 = x - 105

19.2 = x - 105

x = 19.2 +105

x =124.2