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Number of Stamps - GMAT Prep Question - Please help

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by rjanardhanan » Tue Feb 14, 2012 8:13 pm
The number of stamps that Kaye and Alberto had were in the ratio 5:3 respectively.After Kaye gave Alberto 10 of her stamps,the ratio of the number Kaye had to the number Alberto had was 7:5.As a result of this gift,Kaye had how many more stamps than Alberto?

20
30
40
60
90
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by Anurag@Gurome » Tue Feb 14, 2012 8:20 pm
rjanardhanan wrote:The number of stamps that Kaye and Alberto had were in the ratio 5:3 respectively.After Kaye gave Alberto 10 of her stamps,the ratio of the number Kaye had to the number Alberto had was 7:5.As a result of this gift,Kaye had how many more stamps than Alberto?

20
30
40
60
90
Let us assume that Kaye and Alberto now have 7x and 5x stamps respectively. Hence, now Kaye has 2x more stamps than Alberto.

Now, before Kaye gave Alberto 10 stamps, Kaye had (7x + 10) stamps and Alberto had (5x - 10).

So, (7x + 10)/(5x - 10) = 5/3
(21x + 30) = (25x - 50)
4x = 80
2x = 40

The correct answer is C.
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by dhiren8182 » Tue Feb 14, 2012 8:42 pm
Hi Anurag,
I solved it in some other way.
Is this right or wrong?

No of stamps Kaye and Alberto had be 5x and 3x respectively.
Now Kaye gives away 10 stamps so no of stamps Kaye has is 5x-10 and that Alberto has is 3x+10
So 5x-10/3x+10=7/5
=>25x-50=21x+70
=>4x=120
=>x=30
Substituting value of x in 5x-10 we 140 and substituting value of x in 3x+10 we get 100.
Difference of two=40 so Ans is D.
Is this the right approach.
Dhiren
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by GMATGuruNY » Tue Feb 14, 2012 8:48 pm
I posted an alternate solution here:

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by Anurag@Gurome » Tue Feb 14, 2012 9:02 pm
dhiren8182 wrote:Hi Anurag,
I solved it in some other way.
Is this right or wrong?

No of stamps Kaye and Alberto had be 5x and 3x respectively.
Now Kaye gives away 10 stamps so no of stamps Kaye has is 5x-10 and that Alberto has is 3x+10
So 5x-10/3x+10=7/5
=>25x-50=21x+70
=>4x=120
=>x=30
Substituting value of x in 5x-10 we 140 and substituting value of x in 3x+10 we get 100.
Difference of two=40 so Ans is D.
Is this the right approach.
Dhiren
This approach is also correct Dhiren, the correct answer is C, not D.
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by LalaB » Tue Feb 14, 2012 10:53 pm
dhiren8182 wrote:Hi Anurag,
I solved it in some other way.
Is this right or wrong?

No of stamps Kaye and Alberto had be 5x and 3x respectively.
Now Kaye gives away 10 stamps so no of stamps Kaye has is 5x-10 and that Alberto has is 3x+10
So 5x-10/3x+10=7/5
=>25x-50=21x+70
=>4x=120
=>x=30
Substituting value of x in 5x-10 we 140 and substituting value of x in 3x+10 we get 100.
Difference of two=40 so Ans is D.
Is this the right approach.
Dhiren
or

x=30

we need to find (5x-10)-(3x+10)=2x-20 =2*30-20=40
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by gmattesttaker2 » Sat Oct 06, 2012 7:46 am
Hello,

I tried to solve as follows:

K:A = 5x - 10 : 3x + 10

5x - 10
-------- = 7/5
3x + 10

So, x = 30


Now, 7x/5x = 7(30)/5(30)= 210/150

So, Kaye has 60 more stamps than Alberto. I was just wondering why plugging in x in 7x/5x is in-correct? Thanks for your help.

Best Regards,
Sri
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by tisrar02 » Wed Jan 23, 2013 4:41 pm
Well you were correct all the way up until you had to sub X=30 back into the equation.

K= 5(30)-10= 140

A= 3(30)+10= 100

Thus you have a difference of 40. Answer choice C
gmattesttaker2 wrote:Hello,

I tried to solve as follows:

K:A = 5x - 10 : 3x + 10

5x - 10
-------- = 7/5
3x + 10

So, x = 30


Now, 7x/5x = 7(30)/5(30)= 210/150

So, Kaye has 60 more stamps than Alberto. I was just wondering why plugging in x in 7x/5x is in-correct? Thanks for your help.

Best Regards,
Sri
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