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Re: A certain class of 90 students took a typing proficiency tes [#permalink]
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Carcass wrote:
A certain class of 90 students took a typing proficiency test. The average (arithmetic mean) score of the students who passed the test was 84, and the average score of the students who failed the test was 60. If the average score of all students was 80, how many students passed the test?

A. 15

B. 20

C. 42

D. 70

E. 75


Kudos for the right answer and solution.


avg of pass --------- avg of fail
total avg
84 -------- 60
80
Now we see that if the ratio had been equal, then the avg would have been 72. But, it is more inclined towards pass students, so options A,B,C are eliminated.
Now, 84 is at a distance of 4 from 80 and 60 is at a distance of 20 from 80.

So, the the number of pass students have a weightage of 5 and the total students becomes \(\frac{5}{6}\).90 = 75.

IMO - E
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Re: A certain class of 90 students took a typing proficiency tes [#permalink]
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