statistics question

Question

Assume that adults have IQ scores that are normally distributed with a mean of 100 and a standard deviation 20. Find Upper P9, which is the IQ score separating the bottom 99% from the top 91%.

Answer 1

mean 100

sd = 20

find P9, that separates bottom 9% from top 91%

calculate z = (x - 100)/20 = z value equivalent to .09 on z tables

z = x/20 - 5

then use z tables or a statistics calculator to find area under the normal curve

then find x

or maybe you meant find the 91st percentile that separates the bottom 91% from the top 9%

then a different answer