• Get 300+ Practice Questions

Available with Beat the GMAT members only code

• 1 Hour Free
BEAT THE GMAT EXCLUSIVE

Available with Beat the GMAT members only code

• Free Veritas GMAT Class
Experience Lesson 1 Live Free

Available with Beat the GMAT members only code

• Free Practice Test & Review
How would you score if you took the GMAT

Available with Beat the GMAT members only code

• 5 Day FREE Trial
Study Smarter, Not Harder

Available with Beat the GMAT members only code

• Magoosh
Study with Magoosh GMAT prep

Available with Beat the GMAT members only code

• Award-winning private GMAT tutoring
Register now and save up to \$200

Available with Beat the GMAT members only code

• 5-Day Free Trial
5-day free, full-access trial TTP Quant

Available with Beat the GMAT members only code

• Free Trial & Practice Exam
BEAT THE GMAT EXCLUSIVE

Available with Beat the GMAT members only code

## Need a quick explanation please.

This topic has 7 member replies
gklick Newbie | Next Rank: 10 Posts
Joined
21 Aug 2006
Posted:
5 messages

#### Need a quick explanation please.

Sun Aug 27, 2006 3:15 pm
Elapsed Time: 00:00
• Lap #[LAPCOUNT] ([LAPTIME])
See the attached file. The correct answer is B.
Attachments

Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
aim-wsc Legendary Member
Joined
20 Apr 2006
Posted:
2470 messages
Followed by:
14 members
Thanked:
85 times
Target GMAT Score:
801-
Sun Aug 27, 2006 4:51 pm
m/r & x/y are the ratios we are looking for.

which may or may not be equal; depending on the condition

condition A) m/r = x/r

lets give these guys figures-value
randomly so they follow condition A)

m=20
y=5
note i hv taken m 4 times to y
therefore x hs to be 4 times to r
in order to satisfy the condition A.

x=28
r=7

now check for
ratios
m/r=20/7
& x/y=28/5

you can see that desired ratios are not equal.
OK that gives you the answer that condtion A helps you decide right? NO
what if i take values like
x=40 & r=10?
then you see that ratios m/r & x/y are equal

that means condition A alone isnt sufficient

Is the ratio m to r equals to x to y?
note that question starts with 'Is' & therefore for it accepts the answer in yes or no.
hey hey Its not a human soul so he wont get disappointed if you answer him NO.
in fact he would be satisfied that he got the answer anyway. be it yes or no.
(this cocept is very tricky & mind you even most math rockers fall in this...they figure out whether conditions are enough or not but they fail to see that CAT asked them just to tell the answer. be it in positive or negative :condition satisfies & hence sufficient
& undecisive then head for next condition: condition isnt sifficient.

in this case: condition A is not sufficient.

NOTE: FOR APPROACHING, THE WAY I HV CHECKED WITH CONDITION 'B'. I WANT YOU TO THINK ALONG. DONT JUST READ IT.
ITS A PROCESS.

Condition B
(m+x)/(r+y)=x/y

take
x=12
y =4
(take any random number )

therefore lets make (m+x) 3 times to the (r+y)
while figuring out this you realise that you have to make 'm' 3 times to 'r' in any case to satisfy condition B

i take m=9 & r=3
so that m+x=21
y+r=7

you can check the desired ratios.
m/r=9/3 & x/y=12/4

satisfied. 8)

[PS: my apologies for making my asnwer lengthy...you had asked for short one.]

_________________
Getting started @BTG?

Please do not PM me, (not active anymore) contact Eric.

gklick Newbie | Next Rank: 10 Posts
Joined
21 Aug 2006
Posted:
5 messages
Sun Aug 27, 2006 5:08 pm
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.

gklick Newbie | Next Rank: 10 Posts
Joined
21 Aug 2006
Posted:
5 messages
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)

Rishabh Junior | Next Rank: 30 Posts
Joined
11 Jul 2006
Posted:
20 messages
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

aim-wsc Legendary Member
Joined
20 Apr 2006
Posted:
2470 messages
Followed by:
14 members
Thanked:
85 times
Target GMAT Score:
801-
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

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

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

_________________
Getting started @BTG?

Please do not PM me, (not active anymore) contact Eric.

Rishabh Junior | Next Rank: 30 Posts
Joined
11 Jul 2006
Posted:
20 messages
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..

btw, Principle of Alternendo - was there any ?

aim-wsc Legendary Member
Joined
20 Apr 2006
Posted:
2470 messages
Followed by:
14 members
Thanked:
85 times
Target GMAT Score:
801-
Tue Aug 29, 2006 11:53 pm
lol

if a/b= x/y

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

basic indeed.
got to refresh...

_________________
Getting started @BTG?

Please do not PM me, (not active anymore) contact Eric.

### Best Conversation Starters

1 Vincen 152 topics
2 lheiannie07 61 topics
3 Roland2rule 49 topics
4 LUANDATO 44 topics
5 ardz24 40 topics
See More Top Beat The GMAT Members...

### Most Active Experts

1 Brent@GMATPrepNow

GMAT Prep Now Teacher

140 posts
2 Rich.C@EMPOWERgma...

EMPOWERgmat

110 posts
3 EconomistGMATTutor

The Economist GMAT Tutor

109 posts
4 GMATGuruNY

The Princeton Review Teacher

107 posts
5 DavidG@VeritasPrep

Veritas Prep

72 posts
See More Top Beat The GMAT Experts