percentile rank

Griz

New Member
#1
I need to know with a mean of 500 and a standard deviation of 100 how I would find the percentile ranking for the top 10% of a group.... AAAAAAAAGGG
 

Griz

New Member
#2
When I tell you I have put time and effort into this problem, I'm not being glib... OK, what don't I know...

I know Xbar = 500
I know S = 100 (where S = standard deviation)
I know X = raw score

I'm not sure how to solve for X... I drew a normal distribution curve with 500 in the center depicting the mean, but then was unsure what to do with my S... so I abandoned that idea

I tried to think about creating a percentile ranking for the whole deal so I could figure out what the top 10% would be but I somehow missed that part of the lecture, and I can't find it in the text book. Should I be finding a critical area of 10%...? or split for a two tail? Using a Z score? I'm so confused!!! (By the way I have emailed the instructor, but I'm afraid I don't hold out much hope there).

I simply am stuck. this question was on our first quiz and has haunted me now into the latter part of our course... our classes move at such a pace that I would never dream of bringing it up IN class and by the time the class is over, I'm done, stick a fork in me, done... so I thought I'd research it a bit and I found this website. I can understand you not wanting to do everyone's homework for them, nor should you.... I'm just looking for the path to solving this one for my own satisfaction.

Would appreciate any direction. Thanks
 

Griz

New Member
#3
answer to percentile rank

convert the raw score to a z-score and then find the appropriate area under the curve. Multiply this proportion by 100 and you should get the %-ile ranking for that score. Remember the z-distribution is a normal curve and that 50% of cases fall below and above its mean.

*griz* takes a bow :)