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How to resolve propotion?

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by Fokin » Wed Apr 21, 2010 6:34 pm
How to resolove that proportion , i've tried picking numbers but is unsuccessfull^

If w, x, y and z are positive and w/x=y/z, which of the following is not always true ?

a)wz=xy

b) x/w=z/y

c)x/y=z/w

d)(w+x)/z=(y+z)/z

e) (x+w)/w=(z+y)/y

Right answer - C
Last edited by Fokin on Wed Apr 21, 2010 11:09 pm, edited 1 time in total.
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Source: — Data Sufficiency |

by tpr-becky » Wed Apr 21, 2010 10:53 pm
I think you mistyped the problem if the actual problem is w/x=y/z then the problem makes sense. You can pick numbers as you suggested but you can also manipulate the equation by cross multiplying

a) this is obtained by multiplying both sides by x and then by z (w=(y)(x)/z turns inot wz=yx)
b) if you use the equation from ( a) you can divide by w and then divide by y: (z=yx/w turns into z/y=x/w)
c) you cannot manipulate the equation to get this answer
e) this simplifies to x/w+1=z/y+1 which further simplifies to x/w=z/y (the same equation as in b)
Becky
Master GMAT Instructor
The Princeton Review
Irvine, CA
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by eaakbari » Thu Apr 22, 2010 2:13 am
a) Cross multiply
b) reciprocal
c) Aha!
d)Componendo
e) Reciprocal and then Componendo


Hence answer C

Note
Compnendo is
If a/b = c/d
then
(a+b)/b = (c+d)/d
HTH
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- Henry Ford
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by eaakbari » Thu Apr 22, 2010 2:14 am
As a side note, Post your question in the correct forum, this question belongs in PS
Whether you think you can or can't, you're right.
- Henry Ford
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by ajith » Thu Apr 22, 2010 6:06 am
eaakbari wrote:As a side note, Post your question in the correct forum, this question belongs in PS
Moved to PS Forum
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