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Need a quick explanation please.

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gklick Newbie | Next Rank: 10 Posts Default Avatar
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Need a quick explanation please.

Post Sun Aug 27, 2006 3:15 pm
See the attached file. The correct answer is B.
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aim-wsc Legendary Member
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Post Tue Aug 29, 2006 10:04 am
thats right.

& if you know that principle then you wouldnt hv asked the question in first place....


but rishab, it s i think 8 grade high school math. isnt it?

man !!!
principles of Principle of componendo
thats the term right>>?

ok
i m quite old now Mad Evil or Very Mad Crying or Very sad

dont remember any highschool math.. Sad
so i had to solve it emperically.

bytheway....can you tell me Rishab,
what theres some terms like alternando...dividendo.......sigh Exclamation
i dont remember them now...they are all brothers right./?

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Rishabh Junior | Next Rank: 30 Posts Default Avatar
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Post Tue Aug 29, 2006 11:33 pm
Hi,

I remember only a few of them now...

Principle of componendo:
a/b = c/d
=> a+b/b = c+d/d

Principle of dividendo:
a/b = c/d
=> a-b/b = c-d/d

and in ratios & proportions:
a:b :: c:d
product of means = product of extremes
=> a*d = b*c

and GMAT tries to test on such things which actually are very basic..Sad

btw, Principle of Alternendo - was there any ?

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aim-wsc Legendary Member
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Post Tue Aug 29, 2006 10:04 am
thats right.

& if you know that principle then you wouldnt hv asked the question in first place....


but rishab, it s i think 8 grade high school math. isnt it?

man !!!
principles of Principle of componendo
thats the term right>>?

ok
i m quite old now Mad Evil or Very Mad Crying or Very sad

dont remember any highschool math.. Sad
so i had to solve it emperically.

bytheway....can you tell me Rishab,
what theres some terms like alternando...dividendo.......sigh Exclamation
i dont remember them now...they are all brothers right./?

_________________
Getting started @BTG?
Beginner's Guide to GMAT | Beating GMAT & beyond
Please do not PM me, (not active anymore) contact Eric.

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Rishabh Junior | Next Rank: 30 Posts Default Avatar
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Posted:
20 messages
Post Tue Aug 29, 2006 11:33 pm
Hi,

I remember only a few of them now...

Principle of componendo:
a/b = c/d
=> a+b/b = c+d/d

Principle of dividendo:
a/b = c/d
=> a-b/b = c-d/d

and in ratios & proportions:
a:b :: c:d
product of means = product of extremes
=> a*d = b*c

and GMAT tries to test on such things which actually are very basic..Sad

btw, Principle of Alternendo - was there any ?

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aim-wsc Legendary Member
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Post Tue Aug 29, 2006 11:53 pm
lol

Laughing

if a/b= x/y

a+b / a-b = x+y / x-y

basic indeed.Shocked
got to refresh...

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Rishabh Junior | Next Rank: 30 Posts Default Avatar
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Post Tue Aug 29, 2006 4:10 am
Hi,

We have been given
B) (m + x) / (r + y) = x / y
and we have to check if m/r = x/y

Soln: We can write
m/r = x/y
=> m/x = r/y
=> m+x/x = r+y/y (Principle of componendo)
=> m+x/r+y = x/y - same as B

Hence proced mathematically

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gklick Newbie | Next Rank: 10 Posts Default Avatar
Joined
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Posted:
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Post Sun Aug 27, 2006 5:37 pm
gklick wrote:
Thanks, that does make sense. Any idea how to prove it mathematically w/o substitution? If no, that's okay, this explanation is better than no explanation.
Actually, for some reason, I just got it. I have no idea why this was difficult initially.

Given: (m + x) / (r + y) = x / y

x (r + y) = y (m + x)
xr + xy = my + xy
xr = my
(m/r) = (x/y)

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