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# The ratio of the number of red cars in a certain parking lot

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Manager
Joined: 06 Apr 2010
Posts: 139
The ratio of the number of red cars in a certain parking lot [#permalink]

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26 Sep 2010, 10:34
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Difficulty:

5% (low)

Question Stats:

90% (00:29) correct 10% (01:41) wrong based on 276 sessions

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The ratio of the number of red cars in a certain parking lot to the number of black cars is 3 to 8. If there are 72 black cars in the lot, how many red cars are there in the lot?

A. 11
B. 15
C. 24
D. 27
E. 32

I arrivied at answer D, but OA is diff. Please explain where is the trap?
[Reveal] Spoiler: OA

Last edited by Bunuel on 12 Jan 2014, 05:02, edited 1 time in total.
Edited the OA.
Math Expert
Joined: 02 Sep 2009
Posts: 43866
Re: Black-red Car [#permalink]

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26 Sep 2010, 10:36
udaymathapati wrote:
The ratio of the number of red cars in a certain parking lot to the number of black cars is 3 to 8. If there are 72 black cars in the lot, how many red cars are there in the lot?
A. 11
B. 15
C. 24
D. 27
E. 32

I arrivied at answer D, but OA is diff. Please explain where is the trap?

$$\frac{red}{black}=\frac{3x}{8x}$$ --> $$black=8x=72$$ --> $$x=9$$ --> $$red=3x=27$$.

Answer: D (C is not correct).

Moreover if $$red=24$$ then $$\frac{red}{black}=\frac{24}{72}=\frac{3}{9}$$ and not $$\frac{3}{8}$$.

Hope it helps.
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Manager
Joined: 22 Aug 2008
Posts: 181
Re: Black-red Car [#permalink]

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26 Sep 2010, 19:04
D is correct

R/B = 3/8 and B =72
R = 72*3/8 = 27
Intern
Joined: 06 Jan 2014
Posts: 42
Re: The ratio of the number of red cars in a certain parking lot [#permalink]

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12 Jan 2014, 09:56
1
KUDOS
Simply put

$$\frac{3}{8}$$ = $$\frac{X}{72}$$

Cross Multiply so that

$$216=8x$$

x=27
SVP
Joined: 08 Jul 2010
Posts: 1955
Location: India
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WE: Education (Education)
Re: The ratio of the number of red cars in a certain parking lot [#permalink]

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22 Dec 2015, 00:41
udaymathapati wrote:
The ratio of the number of red cars in a certain parking lot to the number of black cars is 3 to 8. If there are 72 black cars in the lot, how many red cars are there in the lot?

A. 11
B. 15
C. 24
D. 27
E. 32

I arrivied at answer D, but OA is diff. Please explain where is the trap?

Black car which is represented by 8 in ratio has actual value = 72 ----- (i.e. 8 x9)

Therefore, Red car which is represented by 3 in ratio will have actual value = 3x9 = 27 ----- (i.e. 3 x9)

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Re: The ratio of the number of red cars in a certain parking lot [#permalink]

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13 Jan 2018, 09:14
Expert's post
Top Contributor
udaymathapati wrote:
The ratio of the number of red cars in a certain parking lot to the number of black cars is 3 to 8. If there are 72 black cars in the lot, how many red cars are there in the lot?

A. 11
B. 15
C. 24
D. 27
E. 32

We can use equivalent ratios here
red/black: 3/8 = x/72
Cross multiply to get: 8x = (3)(72)
Divide both sides by 8 to get: x = (3)(9)
x = 27

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Re: The ratio of the number of red cars in a certain parking lot   [#permalink] 13 Jan 2018, 09:14
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# The ratio of the number of red cars in a certain parking lot

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