At a certain high school, the junior class is twice the size

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At a certain high school, the junior class is twice the size [#permalink]

21 May 2012, 05:29

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At a certain high school, the junior class is twice the size of the senior class. If 1/3 of the seniors & 1/4 of the juniors study Japanese, what fraction of the students in both classes do not study Japanese?

A. 1/6
B. 5/18
C. 5/12
D. 7/12
E. 13/18

Is it possible to do as follows?
1/3*s+1/4*2s = study japanese
then 5/6 * s = study japanese and 1/6 do not
why is this wrong?

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Re: At a certain high school, the junior class is twice the size [#permalink]

21 May 2012, 06:25

kashishh wrote:

If we do the way you proposed then the # of the students that study Japanese is 1/3*s+1/4*2s=5s/6. Since the total # of the students is s+2s=3s then the # of the students that does not study Japanese is 3s-5s/6=13s/6, so fraction of the students that do not study Japanese is (13s/6)/3s=13/18.

Answer: E.

Else you can do as follows: say there are 6 seniors and 2*6=12 juniors, so total of 6+12=18 students.

2/3 of the seniors do not study Japanese, so 2/3*6=4 seniors do not study Japanese;
3/4 of the juniors do not study Japanese, so 3/4*12=9 juniors do not study Japanese;

Total of 4+9=13 students do not study Japanese, which is 13/18 of all students.

Answer: E.

Hope it helps.
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Re: At a certain high school, the junior class is twice the size [#permalink] 21 May 2012, 06:25

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At a certain high school, the junior class is twice the size

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At a certain high school, the junior class is twice the size

At a certain high school, the junior class is twice the size

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