Amy's grade was the 90th pencentile of the 80 grades for her class. Of the 100 grades from another class,19 were higher than Amy's, and the rest were lower . If no other grade was the same as Amy's grade, the amy's grade was what percentile of the grades of the two classes combined.
可以这样想， her ranking in her class is 90x80%=72, 8 persons are aheard of her; In another class, 19 persons are ahead of her, combined with two classs, there are total 80+100=180 persons, but 8+19 = 27 persons are ahead of her, so, she is ranking at (180-27)/180= 85% in two classes.
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发表于 2008-7-9 23:09:00
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