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by kartik r - Wednesday, 22 December 2010, 09:50 PM
  I received a rather rude surprise during my second diagnostic test, which i wrote. The first question of the exam was something on percentiles and I haven't found this topic discussed anywhere at all. I've finished portions from the Kaplan math workout book and princeton review.

Could I request the math gurus to enlighten me on this topic?

As an aside, the question that I was stumped with is as follows:

Angela’s grade was in the 90th percentile out of 80 grades in her class. In another class of 100 students there were 19 grades higher than Angela’s. If nobody had Angela’s grade, then Angela was what percentile of the two classes combined?

a. 72
b. 80
c. 81
d. 85
e. 92

The correct answer I believe is 85, yet I don't know how one arrives at this conclusion.

thanks a ton

Re: Percentile
by amit jha - Thursday, 23 December 2010, 09:06 AM
  in first class her score is 90th percentile meaning 10 students are ahead of her in 100.
And so in class of 80 there are 8 students ahead of her.

Now in second class there are 19 ahead of her.

So in 180 there are 27 ahead of her,
which would translate in 100 as : (27/180)* 100 = 15

That clearly means her percentile should be 85

Re: Percentile
by Govi Ravi - Sunday, 23 January 2011, 01:37 AM
  You can use weighted average concept here!!

(90 * 80 + 100 * 81) /(80+100)

SOlving we get 85.