# Normal distribution

• Oct 3rd 2011, 12:14 PM
Girlaaaaaaaa
Normal distribution
I have a question about how to show the work for this and how to solve it also
Here is the problem:
The verbal part of the GRE has a mean of 500 and a standard deviation of 100. Use the normal distribution to answer the questions:
a. if we wanted to select only students at or above the 90th percentile, what verbal gre score would we use as a cutoff? I got the answer 628.01 but unsure about how to show my work
b.what verbal gre score corresponds to a percentile rank of 15%. 55%?
c what is the precentile rank of a verbal gre score of 628? 350?
d if we randomly selcted 1,500 students who had taken the verbal gre how many would we expect to score lower than 250? higher than 750?
• Oct 3rd 2011, 01:06 PM
pickslides
Re: Normal distribution
For he first one...

$\displaystyle \displaystyle P\left( Z> \frac{x-500}{100}\right) = 0.9$
• Oct 3rd 2011, 01:09 PM
Girlaaaaaaaa
Re: Normal distribution
how would that be worked out?
• Oct 3rd 2011, 01:14 PM
pickslides
Re: Normal distribution
In the normal distribution table, find the value of $\displaystyle \displaystyle Z_0$ such that

$\displaystyle \displaystyle P\left( Z> Z_0) = 0.9$

Make the result equal to $\displaystyle \displaystyle \frac{x-500}{100}$ and solve for $\displaystyle x$