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Something about Percentile Ranks and Percentages



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Gender: Female
Points: 890
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Sun Oct 08, 2006 7:19 am
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Elizabeth says...



Alright... so here.s something from my stupid 9th Grade DISCOVERING ADVANCED ALGEBRA 3/ TRIG.

I need help with finding percentile rates and percentages. The only thing I know about percentiles is that there is no 0 or 100, there's only 1-99.

I already asked Snoink about this, but I got too confused still... I'll give the problem and the parts to it.


At a large university, 1,500 students took a final exam in chemistry.

A) Frank learns taht his score of 76 (out of 100) places him in the 88th percentile. How many students scored lower than Frank? How many scored Higher?


My Answer: 1139/1140/1141 people scored below the 88th percentile rank. 359/360/361 scored above him.

(The real reason I have 3 numbers is I can't tell which one to use, because Frank is involved too, can't forget about him... but I'm thinking he scored more than 1139 and less than 361)

B) Mary scored 82, which placed her at the 95th percentile. Describe how Mary's performance compares to that of the others in the class.

My Answer:
I got confused... compare with words or with numbers? So... didn't write anything here. (I'm a hopeless cause)

C) The highest score on the exam was 91. What percentile rank is associated with this score?

My Answer:
I got 91st. Because the equation, on a link Snoink gave me, said that it was the amount of people below, divided by the total, times 100. So I had.

(1365/1500)100 = .91

Did I do this right? Is this the percentile rank, 91?

D) Every student who scored above the 90th percentile recieved an A. How many students earned this grade?

My Answer:
I figured out how big the frequencey was for 1 percentile, which was 15 and multiplied that by 90 (which was 1% less than the above percentile rank, if I even got that right) then subtracted it from 1500 and got 150 students= who scored above the percentile rank.

1500-(15x90)=150


I would like equations and to know if I did this right, because if I did then I'll try and remember WHAT I did to be able to do what I did :P.

I'm not even 15 yet and my parent's haven't been able to help me with my homework since I was 12, so please somebody help me! Of course on Monday is a review but I'd like to knwo now and show off to the teacher :P.

Thank you, Elizabeth
  





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Gender: Female
Points: 890
Reviews: 10
Mon Oct 09, 2006 11:49 pm
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Max McKali says...



lol, i feel your pain. we did this last year and all i remember was something about a curve...r u using the curve? it looks something like this and it tells u what percent is in each percentile:

http://www.stat.wmich.edu/s216/exam1rev ... s/q5c2.gif
"All for one and one for all- that is our motto, is it not?"
  





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Gender: Female
Points: 890
Reviews: 1160
Tue Oct 10, 2006 8:41 pm
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Elizabeth says...



She brings up the curve now and then but... I dont' get it!
  








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