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Ratio question

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manjeshmurthy
 Post subject: Ratio question
 Post Posted: Wed Jan 05, 2011 4:02 am 
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Course Students


Posts: 7
Hello Instructors,

source from mba.com practice test

Number of stamps that kaye & albero had were 5:3, after Kaye gave Alberto 10 of her stamps. the ratio of number of stamps kaye had to number of stamps alberto had was 7:5. As a result of this gift, kaye had how many more stamps than alberto

a) 20 b) 30 c) 40 d)60 e) 90

i tried solving by (5x-10)/(3x-10) = 7/5 , where i got x = 5, but was not sure how to proceed further or the approach is right

so can you guys show the way to solve this

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Quest4GMAT
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jnelson0612
 Post subject: Re: Ratio question
 Post Posted: Wed Jan 05, 2011 9:21 am 
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ManhattanGMAT Staff


Posts: 1857
manjeshmurthy wrote:
Hello Instructors,

source from mba.com practice test

Number of stamps that kaye & albero had were 5:3, after Kaye gave Alberto 10 of her stamps. the ratio of number of stamps kaye had to number of stamps alberto had was 7:5. As a result of this gift, kaye had how many more stamps than alberto

a) 20 b) 30 c) 40 d)60 e) 90

i tried solving by (5x-10)/(3x-10) = 7/5 , where i got x = 5, but was not sure how to proceed further or the approach is right

so can you guys show the way to solve this


manjesh,
We have a forum for questions from the mba.com test--it is called GMAT Prep Math and here is the link: gmat-prep-math-f30.html

Will you please post this question in that forum? Someone will help you there and I will delete this thread. Thank you.

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Jamie Nelson
ManhattanGMAT Instructor
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gokyada
 Post subject: Re: Ratio question
 Post Posted: Wed Jan 05, 2011 1:24 pm 
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Course Students


Posts: 7
Given
K/A = 5/3 which is 3K = 5A

(K-10)/(A+10) = 7/5, which is 5K-7A = 120

Solve above for K and A.
K = 150, A = 90

Kayle current stamps = K-10 = 140
Al current stamps = A+10 = 100

So Kayle has 40 more stamps. (C)
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manjeshmurthy
 Post subject: Re: Ratio question
 Post Posted: Wed Jan 05, 2011 2:03 pm 
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Course Students


Posts: 7
Thanks Jamie & gokyada,

you could remove the thread, just let me quickly wrap this up , as gokyada has answer to this..

so gokyada..

how is (K-10)/ (A+10) = 7/5 is it not that it has to be 5K-10 & 3A+10 . since there ratio is 5:3

since the Kaye had 3x ( where x is multiplier) not just x stamps.
& the total number of stamps is not changing.. as there is no extra stamps added.
rest is clear to me..

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Quest4GMAT
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jnelson0612
 Post subject: Re: Ratio question
 Post Posted: Sun Jan 09, 2011 2:58 pm 
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ManhattanGMAT Staff


Posts: 1857
manjeshmurthy wrote:
Thanks Jamie & gokyada,

you could remove the thread, just let me quickly wrap this up , as gokyada has answer to this..

so gokyada..

how is (K-10)/ (A+10) = 7/5 is it not that it has to be 5K-10 & 3A+10 . since there ratio is 5:3

since the Kaye had 3x ( where x is multiplier) not just x stamps.
& the total number of stamps is not changing.. as there is no extra stamps added.
rest is clear to me..


manjesh,
Let me jump back in here. gokyada has solved this perfectly. He is using K and A to signify exactly how many stamps each person was originally holding. We know that the ratio of these numbers is 5:3. Thus, since K and A stand for the exact values of stamps each person has, (K-10)/(A+10) = 7/5 also perfectly expresses the result after Kaye gives Alberto 10 of her stamps. We can then use our knowledge of 3K=5A to solve for one of the variables, and after we obtain one variable we can calculate the other. If you plug the values back in for K and A everything works out exactly. You really don't need to use the unknown multiplier in this equation since K and A can stand in for the actual numbers.

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Jamie Nelson
ManhattanGMAT Instructor
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