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# The ratio of boys to girls in a class is 3 to 5. If 2 boys are added t

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The ratio of boys to girls in a class is 3 to 5. If 2 boys are added t  [#permalink]

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10 May 2020, 07:31
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The ratio of boys to girls in a class is 3 to 5. If 2 boys are added to the class and 6 girls leave the class, the new ratio of boys to girls is 5 to 6. How many girls were in the class to begin with?
A) 15
B) 20
C) 25
D) 30
E) 35
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The ratio of boys to girls in a class is 3 to 5. If 2 boys are added t  [#permalink]

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Updated on: 10 May 2020, 07:50
The ratio of boys to girls in a class is 3 to 5. If 2 boys are added to the class and 6 girls leave the class, the new ratio of boys to girls is 5 to 6. How many girls were in the class to begin with?
A) 15
B) 20
C) 25
D) 30
E) 35

Boys = 3x
Girls = 5x

(3x+2):(5x-6) = 5:6

i.e. 18x+12 = 25x-30

i.e. 7x = 42

i.e. x = 6

Girls in beginning = 5x = 30

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Originally posted by GMATinsight on 10 May 2020, 07:34.
Last edited by GMATinsight on 10 May 2020, 07:50, edited 1 time in total.
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Re: The ratio of boys to girls in a class is 3 to 5. If 2 boys are added t  [#permalink]

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10 May 2020, 07:47
1
GMATinsight ; see highlighted part

GMATinsight wrote:
The ratio of boys to girls in a class is 3 to 5. If 2 boys are added to the class and 6 girls leave the class, the new ratio of boys to girls is 5 to 6. How many girls were in the class to begin with?
A) 15
B) 20
C) 25
D) 30
E) 35

Boys = 3x
Girls = 5x

(3x+2):(5x-6) = 5:6

i.e. 18x+12 = 25x-30

i.e. 7x = 42

i.e. [highlight]x = 7
[/highlight]

Girls in beginning = 5x = 35

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The ratio of boys to girls in a class is 3 to 5. If 2 boys are added t  [#permalink]

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10 May 2020, 07:49
The ratio of boys to girls in a class is 3 to 5. If 2 boys are added to the class and 6 girls leave the class, the new ratio of boys to girls is 5 to 6. How many girls were in the class to begin with?
A) 15
B) 20
C) 25
D) 30
E) 35

given
boys/girls = 3/5
b= 3g/5
also
b+2/g-6 = 5/6
6b+12 = 5g-30
solve for g
18g/5-5g = -42
18g-25g = -42 *5
-7g = -42*5
g= 30

OPTION D
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Re: The ratio of boys to girls in a class is 3 to 5. If 2 boys are added t  [#permalink]

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10 May 2020, 07:54
The ratio of boys to girls in a class is 3 to 5. If 2 boys are added to the class and 6 girls leave the class, the new ratio of boys to girls is 5 to 6. How many girls were in the class to begin with?
A) 15
B) 20
C) 25
D) 30
E) 35

$$\frac{b}{g} = \frac{3x}{5x}$$

$$\frac{b + 2}{g - 6 } = \frac{3x + 2}{5x - 6 } = \frac{5}{6}$$

Now, $$18x + 12 = 25x - 30$$

Or, $$7x = 42$$

So, $$x = 6$$ , So Number of girls in the beginng is 5*6 = 30, Annswer must be (D) 30
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Re: The ratio of boys to girls in a class is 3 to 5. If 2 boys are added t   [#permalink] 10 May 2020, 07:54