IQ scores that are normally distributed standard deviation

Question

Assume that adults have IQ scores that are normally distributed with a mean of 100100 and a standard deviation 20. Find Upper P3, which is the IQ score separating the bottom 33% from the top 97%.

Answer 1

mean=100

std dev  = 20

 

Let the 3rd percentile be C.

 

P(z< C) = 0.03

C = -2.75

 

-2.75 = (X - 100)/20

 

X = -2.75*20 + 100 = 45