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PS - % of ratio

by karthikpandian19 » Wed Jul 04, 2012 8:53 pm
In a high school algebra class, the ratio of failing to passing grades was 2 to 9 last year. If the ratio of failing to passing grades decreased by 15% this year, what was the ratio of failing to passing grades in the class this year?


(A) 1/30

(B) 3/20

(C) 2/9

(D) 17/90

(E) 17/9
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by theCEO » Wed Jul 04, 2012 9:07 pm
The previous ratio is (100% * (2/9)).
It decreased by 15%: (15% * 2/9)
Its new ratio is (100% - 15%)*2/9 = 85% * 2/9

85/100 * 2/9 = 17/90
ans = d
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by karthikpandian19 » Wed Jul 04, 2012 10:32 pm
Previously i was using another long method.........

Thanks for this short one
theCEO wrote:The previous ratio is (100% * (2/9)).
It decreased by 15%: (15% * 2/9)
Its new ratio is (100% - 15%)*2/9 = 85% * 2/9

85/100 * 2/9 = 17/90
ans = d
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by GMATGuruNY » Thu Jul 05, 2012 3:11 am
karthikpandian19 wrote:In a high school algebra class, the ratio of failing to passing grades was 2 to 9 last year. If the ratio of failing to passing grades decreased by 15% this year, what was the ratio of failing to passing grades in the class this year?


(A) 1/30

(B) 3/20

(C) 2/9

(D) 17/90

(E) 17/9
Let last year's failing grades = 20 and last year's passing grades = 90.
For the ratio to decrease by 15%, the number of failing grades must decrease by .15(20) = 3.
Ratio this year = (20-3)/90 = 17/90.

The correct answer is D.
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by karthikpandian19 » Thu Jul 05, 2012 2:23 pm
OA is D
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Karthik
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