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# THe # of stamps that Kim and Andy had were in the ration

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Manager
Joined: 19 Sep 2005
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THe # of stamps that Kim and Andy had were in the ration [#permalink]  10 Oct 2005, 07:07
THe # of stamps that Kim and Andy had were in the ration 5:3. After Kim gave 10 stamps to Andy, the ration was 7:5.
as a restult of the gift, kim had how mnay more stamps than Andy?
a. 20
b. 30
c. 40
d. 60
e. 90
SVP
Joined: 24 Sep 2005
Posts: 1891
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Re: Ratio question- how do u do it? [#permalink]  10 Oct 2005, 07:20
Jennif102 wrote:
THe # of stamps that Kim and Andy had were in the ration 5:3. After Kim gave 10 stamps to Andy, the ration was 7:5.
as a restult of the gift, kim had how mnay more stamps than Andy?
a. 20
b. 30
c. 40
d. 60
e. 90

let x and y be the stamps of K and A respectively
x:y=5:3---->x=5/3y
(x-10): (y+10)=7:5---->5x-50=7y+70
substitue x by y ,we have : 25/3y-50=7y+70<===> y=90 --->
x=5/3(90)=150
---->x-y=60
D.
Manager
Joined: 04 May 2005
Posts: 133
Location: Chicago
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I got C [#permalink]  10 Oct 2005, 07:34
_________________

Christopher Wilson

Manager
Joined: 06 Oct 2005
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Location: Beantown
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Agree w/ Chris. I got (c), Laxie #'s were before the gift.

B.
Manager
Joined: 03 Oct 2005
Posts: 87
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I was just reading Peterson's the other day and trying to use plugging in to arrive at the answer. And was getting nowhere very fast.

How'd you do it by plugging in?

(Plugging in seems a little unnatural to me - the equation method would work for me.)
SVP
Joined: 24 Sep 2005
Posts: 1891
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Kudos [?]: 159 [0], given: 0

oops, I was too careless as reading the question
Manager
Joined: 10 Sep 2005
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am still lost...

5 /8 (x-10) = 7 /12 (x)
x = 150
2/12 (150) = 25 ( 2 is the diff 7-5 to for the 2nd ratio)

pls i need a simple explanation as 40 is the OA
thks
Current Student
Joined: 28 Dec 2004
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Location: New York City
Schools: Wharton'11 HBS'12
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Kudos [?]: 186 [0], given: 2

K/A=5/3

(K-10)/(A+10)=7/5

now solve for K and A...

once you get K and A, then you minus K-A to get the difference...
Senior Manager
Joined: 02 Oct 2005
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sushom101:

Hope you are clear on this part.

Quote:
let x and y be the stamps of K and A respectively
x:y=5:3---->x=5/3y
(x-10): (y+10)=7:5---->5x-50=7y+70
substitue x by y ,we have : 25/3y-50=7y+70<===> y=90 --->
x=5/3(90)=150
---->x-y=60

We have found x and y. Now kim gave 10 stamps to andy. So the new x = 140 and new y = 100. The difference is 40.

Hope it is clear now.
Current Student
Joined: 29 Jan 2005
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I had the exact same type of question on the official test last month, and probably missed it!
Manager
Joined: 10 Sep 2005
Posts: 164
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hey! got it guys...thanks
GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5068
Location: Singapore
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Assume the number of stamps = n

Initially:
K = 5n/8 stamps
A = 3n/8 stamps

k gave 10 stamps to Andy --> 5n/8 - 10
A got 10 stamps from Kim --> 3n/8 + 10

The new ratio (Kim:Andy) = 7/5 = (5n/8-10)/(3n/8+10)

Solving -> n = 240

Kim now has 7/12 * 240 = 140 stamps
Andy now has 240-140 = 100 stamps

So Kim has 140-100 = 40 stamps more than Andy.
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