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GRE Math Challenge #24-Yesterday, a certain school had

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Director
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GRE Math Challenge #24-Yesterday, a certain school had [#permalink] New post 15 Sep 2014, 13:51
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Question Stats:

47% (00:27) correct 52% (00:36) wrong based on 17 sessions
Yesterday, a certain school had an equal number of boys and girls. Today, 18 boys left the school, and the ratio of the number of boys to girls is now 3 to 4.


Column AColumn B
Number of boys in the school now72


A)The quantity in Column A is greater.
B)The quantity in Column B is greater.
C)The two quantities are equal.
D)The relationship cannot be determined from the information given.
[Reveal] Spoiler: OA

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Re: GRE Math Challenge #24 [#permalink] New post 15 Sep 2014, 22:41
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Yesterday, we have no. of boys (b) = no. of girls (g)=> b=g ----(i)
Today, (b-18) : g = 3:4 => (b-18)/g = 3/4 => 4(b-18) = 3g ----- (ii)

From, equations, (i) & (ii) => 4b - 72 = 3b => b=72 => Yesterday, the number of boys were 72 and today their number has reduced to (72-18) to 54.
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Re: GRE Math Challenge #24-Yesterday, a certain school had [#permalink] New post 08 Mar 2018, 00:48
soumya1989 wrote:
Yesterday, a certain school had an equal number of boys and girls. Today, 18 boys left the school, and the ratio of the number of boys to girls is now 3 to 4.


Column AColumn B
Number of boys in the school now72


A)The quantity in Column A is greater.
B)The quantity in Column B is greater.
C)The two quantities are equal.
D)The relationship cannot be determined from the information given.


First of all, we should set the ratio in terms of scale factor for the numbers of boy to girls yesterday. That is \(\frac{a}{a}\) where the numerator stands for boy.

For today we can set that \(\frac{a-18}{a}\)=\(\frac{3}{4}\).

Then we cross multiply. We get 3a=4a-72, a=72. and today's boy number would be 72-18=54

Thus, B>A
Re: GRE Math Challenge #24-Yesterday, a certain school had   [#permalink] 08 Mar 2018, 00:48
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GRE Math Challenge #24-Yesterday, a certain school had

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