# normal distribution/ z score chart

• Mar 31st 2011, 06:46 PM
miller13
normal distribution/ z score chart
I need help!!!
the verbal part of the graduate record exam(gre) has a mean (u) of 500 and a standard deviation of 100. use the normal distribution to answer the following:
1. if we wanted to select only students at or above the 90th percentile, what verbal gre score would we use as a cutoff?
2. what verbal gre score corresponds to a percentile rank of 15%? 55%?
3. what is the percentile rank of a verbal gre score of 628? 350?
4. if we randomly selected 1,500 students who had taken the verbal gre, how many would we expect to score lower than 250? higher than 750?

i am having issues finding the zscore and then correlating it with the normal distribution chart.. and I am also having issues with the percentile rank... can anyone please help me? it would be greatly appreciated :)
• Mar 31st 2011, 06:56 PM
TheChaz
Quote:

Originally Posted by miller13
I need help!!!
the verbal part of the graduate record exam(gre) has a mean (u) of 500 and a standard deviation of 100. use the normal distribution to answer the following:
1. if we wanted to select only students at or above the 90th percentile, what verbal gre score would we use as a cutoff?
2. what verbal gre score corresponds to a percentile rank of 15%? 55%?
3. what is the percentile rank of a verbal gre score of 628? 350?
4. if we randomly selected 1,500 students who had taken the verbal gre, how many would we expect to score lower than 250? higher than 750?
...

1.
a) look at the z-table and find the z-score closest to 0.9000000000000000000
b) $\displaystyle \frac{x - \mu}{\sigma} = z$
You have three of the values in this formula. Use algebra to solve for the fourth.