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Retired Moderator Joined: 29 Oct 2013
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The ratio of R to S is 3 to 5, what is the value of the rati  [#permalink]

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The ratio of R to S is 3 to 5, what is the value of the ratio (R + K)/(S + K)?

(1) R = 12
(2) K = 7

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Originally posted by NoHalfMeasures on 12 Aug 2014, 02:30.
Last edited by Bunuel on 12 Aug 2014, 02:33, edited 1 time in total.
Edited the question
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Joined: 02 Sep 2009
Posts: 58402
Re: The ratio of R to S is 3 to 5, what is the value of the rati  [#permalink]

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The ratio of R to S is 3 to 5, what is the value of the ratio (R + K)/(S + K)?

R:S = 3:5.

(1) R = 12 --> S = 20. We need K. Not sufficient.

(2) K = 7 --> (R + K)/(S + K) = (R + 7)/(5R/3 + 7). The ratio will change depending on R. Not sufficient.

(1)+(2) We know the values of all variables, thus we can get the desired ratio. Sufficient.

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The ratio of R to S is 3 to 5, what is the value of the rati  [#permalink]

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Hi Bunuel,

Just a silly basic question...

Given that ratio of R to S is 3 to 5, We cannot compute this as 3+7 / 5+7 Correct? Hence "B" would be wrong.

Pls clarify my doubt as in why we cannot compute this as 3+7 / 5+7.

Thanks

Bunuel wrote:
The ratio of R to S is 3 to 5, what is the value of the ratio (R + K)/(S + K)?

R:S = 3:5.

(1) R = 12 --> S = 20. We need K. Not sufficient.

(2) K = 7 --> (R + K)/(S + K) = (R + 7)/(5R/3 + 7). The ratio will change depending on R. Not sufficient.

(1)+(2) We know the values of all variables, thus we can get the desired ratio. Sufficient.

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Joined: 02 Sep 2009
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Re: The ratio of R to S is 3 to 5, what is the value of the rati  [#permalink]

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Buddyisrael wrote:
Hi Bunuel,

Just a silly basic question...

Given that ratio of R to S is 3 to 5, We cannot compute this as 3+7 / 5+7 Correct? Hence "B" would be wrong.

Pls clarify my doubt as in why we cannot compute this as 3+7 / 5+7.

Thanks

Bunuel wrote:
The ratio of R to S is 3 to 5, what is the value of the ratio (R + K)/(S + K)?

R:S = 3:5.

(1) R = 12 --> S = 20. We need K. Not sufficient.

(2) K = 7 --> (R + K)/(S + K) = (R + 7)/(5R/3 + 7). The ratio will change depending on R. Not sufficient.

(1)+(2) We know the values of all variables, thus we can get the desired ratio. Sufficient.

Yes, you are right we cannot do that way.

The ratio of R to S is 3 to 5, does not mean that R is 3 and S is 5, they can be (6, 10), (9, 15), (12, 20)...
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Re: The ratio of R to S is 3 to 5, what is the value of the rati  [#permalink]

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1. R = 12 that gives us S but we do not know K. NS
2. K = 7 but we do not know what is S, S can be 5, 10 15 so no.. NS

1&2. we get R, S and K Sufficient.

MensaNumber wrote:
The ratio of R to S is 3 to 5, what is the value of the ratio (R + K)/(S + K)?

(1) R = 12
(2) K = 7

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Intern  Joined: 31 May 2013
Posts: 12
The ratio of R to S is 3 to 5, what is the value of the rati  [#permalink]

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Folks,

Since R:S::3:5, why can't we use R=3K and S=5K then we don't need information from 1. and 2.
Then shouldn't D. be the answer?

-Thanks
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Re: The ratio of R to S is 3 to 5, what is the value of the rati  [#permalink]

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Reaper wrote:
Folks,

Since R:S::3:5, why can't we use R=3K and S=5K then we don't need information from 1. and 2.
Then shouldn't D. be the answer?

-Thanks

Hi Reaper - if R & S are in a ratio of 3:5, we can surely write them as 3x and 5x respectively. However, in this case we do not know whether x = K. Hence your interpretation of answer being D will not hold.

Let me also explain this with an example. Assume R = 12 and S = 20, then R & S are in the ratio of 3:5. So, R & S can be written as 3x and 5x respectively for x =4. Depending upon the values of R & S, the value of x would vary. For R = 15 & S = 25, value of x would be 5 and so on.

Since we do not know the value of K, we can't say for sure if R=3K and S=5k respectively.

Hope this helps!

Regards
Harsh
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GMAT 1: 800 Q51 V49 GRE 1: Q170 V170 Re: The ratio of R to S is 3 to 5, what is the value of the rati  [#permalink]

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Hi All,

This DS question can be dealt with in a couple of different ways. You can use "math theory" on this prompt, but unless your understanding of the concepts is PERFECT, you might make a little mistake and select an incorrect answer (and not even know it). By TESTing VALUES, you can PROVE the correct answer (and do so with a certain amount of ease).

We're told that the ratio of R to S is 3 to 5. We're asked for the value of (R + K)/(S + K).

Fact 1: R = 12

With the given ratio (R:S = 3:5), we now know that S = 20. We don't know the value of K though...

IF....
K = 0
The answer to the question is (12+0)/(20+0) = 12/20 = 3/5

IF...
K = 1
The answer to the question is (12+1)/(20+1) = 13/21
Fact 1 is INSUFFICIENT

Fact 2: K = 7

We don't know the values of R and S, but we DO know that they fall into the ratio of 3:5......

IF...
R = 3
S = 5
The answer to the question is (3+7)/(5+7) = 10/12 = 5/6

IF...
R = 6
S = 10
The answer to the question is (6+7)/(10+7) = 13/17
Fact 2 is INSUFFICIENT

Combined, we know....
R = 12 (so S = 20)
K = 7

The answer to the question MUST be (12+7)/(20+7) = 19/27
Combined, SUFFICIENT

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Rich
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GMAT 1: 780 Q51 V46 Re: The ratio of R to S is 3 to 5, what is the value of the rati  [#permalink]

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Hi All,
This is a tricky question. Here students may do careless error by chosing D or B.
But the answer is together sufficient:
Ratio of R to S is 3 to 5.
Then value of R to S is 3x to 5x.
Now the question asks for value of the ratio R+k to S+k.
So that’s 3x+k to 5x+k.
We need x and k values.
Statement 1 : Not sufficient:
From statement 2 we only get x value because R= 3x and 3x=12 so x = 4.
But no info about K.
So not sufficient.
Statement 2 : Not sufficient:
Gives the K value and no info about x.
So not sufficient.
Together it is sufficient.
Because we get both x and K values.
So answer is C.
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Re: The ratio of R to S is 3 to 5, what is the value of the rati  [#permalink]

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Yes Harsh, it makes sense. x=K is not definitive.

-Thanks
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Re: The ratio of R to S is 3 to 5, what is the value of the rati  [#permalink]

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