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Manager  Joined: 06 Apr 2010
Posts: 103
The ratio of the number of red cars in a certain parking lot  [#permalink]

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Difficulty:   5% (low)

Question Stats: 92% (00:46) correct 8% (02:11) wrong based on 309 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?

Originally posted by udaymathapati on 26 Sep 2010, 11:34.
Last edited by Bunuel on 12 Jan 2014, 06:02, edited 1 time in total.
Edited the OA.
Math Expert V
Joined: 02 Sep 2009
Posts: 58445
Re: Black-red Car  [#permalink]

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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: 112
Re: Black-red Car  [#permalink]

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D is correct

R/B = 3/8 and B =72
R = 72*3/8 = 27
Intern  Joined: 06 Jan 2014
Posts: 35
Re: The ratio of the number of red cars in a certain parking lot  [#permalink]

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Simply put

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

Cross Multiply so that

$$216=8x$$

x=27
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Re: The ratio of the number of red cars in a certain parking lot  [#permalink]

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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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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, 10:14
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