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# On Monday, a class has 8 girls and 20 boys. On Tuesday, a certain numb

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Math Expert
Joined: 02 Sep 2009
Posts: 56300
On Monday, a class has 8 girls and 20 boys. On Tuesday, a certain numb  [#permalink]

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19 Aug 2018, 09:11
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Difficulty:

45% (medium)

Question Stats:

81% (02:23) correct 19% (03:00) wrong based on 35 sessions

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On Monday, a class has 8 girls and 20 boys. On Tuesday, a certain number of girls joined the class just as twice that number of boys left the class, changing the ratio of girls to boys to 7 to 4. How many boys left the class on Tuesday?

(A) 5
(B) 6
(C) 11
(D) 12
(E) 18

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Re: On Monday, a class has 8 girls and 20 boys. On Tuesday, a certain numb  [#permalink]

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19 Aug 2018, 09:25
Let the number of girls joining the class on Tuesday be X and twice the number of boys leaves the class. Let it be 2X.
Now, $$\frac{{8+X}}{{20-2X}}$$ = $$\frac{7}{4}$$
Solving we get 32+4X = 140-14X
18X = 108.
So X = 6.
Hence the number of boys leaving the class on Tuesday is 2X = 12.
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Re: On Monday, a class has 8 girls and 20 boys. On Tuesday, a certain numb  [#permalink]

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19 Aug 2018, 09:32
Monday: G:B= 8:20
Tuesday : G:B =7:4
As given #girls will increase from Mon to Tue. Tue day ratio is 7:4
=> this indicates #girls on Tues can be 14, lets try with 14,
=> #girls increased by 6, #boys decreased by 12,
=> Tue ratio 14: 8 =7:4
=> Ans 12, D

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Re: On Monday, a class has 8 girls and 20 boys. On Tuesday, a certain numb   [#permalink] 19 Aug 2018, 09:32
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