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Director
Joined: 12 Jun 2006
Posts: 532

If rs#0, is 1/r + 1/s = 4 ? [#permalink]
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11 Jun 2007, 22:19
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74% (01:47) correct
26% (00:49) wrong based on 115 sessions
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If rs#0, is 1/r + 1/s = 4 ? (1) r + s = 4rs (2) r = s OPEN DISCUSSION OF THIS QUESTION IS HERE: ifrs0is1r1s102597.html
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Last edited by Bunuel on 23 Feb 2014, 02:29, edited 2 times in total.
Renamed the topic, edited the question and added the OA.



GMAT Club Legend
Joined: 07 Jul 2004
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Location: Singapore

St1:
r = 4rss = s(4r1)
Insufficient.
St2:
1/r + 1/s = 2/r or 2/s. Insufficient.
Using both, we have, 2s = 4s^2
2s(12s) = 0
s = o (invalid) or s = 1/2 = r. So we can answer the question now. Sufficient.
Ans C



VP
Joined: 10 Jun 2007
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Re: DS: 246 [#permalink]
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11 Jun 2007, 22:26
ggarr wrote: if rs is not equal to 0, is 1/r + 1/s = 4?
1) r+s = 4rs 2) r = s
Please explain your solution
The answer is A.
1) (r+s) / rs = 4
=> (r/rs) + (s/rs) = 4
=> (1/r) + (1/s) = 4
SUFFICIENT
2) plug in r=s=1/2, you get 4=4. But plug in r=s=1, you get 2=4. INSUFFICIENT.



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Re: DS: 246 [#permalink]
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11 Jun 2007, 22:27
bkk145 wrote: ggarr wrote: if rs is not equal to 0, is 1/r + 1/s = 4?
1) r+s = 4rs 2) r = s
Please explain your solution The answer is A. 1) (r+s) / rs = 4 => (r/rs) + (s/rs) = 4 => (1/r) + (1/s) = 4 SUFFICIENT2) plug in r=s=1/2, you get 4=4. But plug in r=s=1, you get 2=4. INSUFFICIENT.
gar!! failed to see that...



Manager
Joined: 17 Oct 2006
Posts: 52

For me the answer is A
r+s=4rs
dividing both sides by rs
r/rs+s/rs=4
1/r+1/s=4 (Sufficient)
r=s
Different values of r or s suggest that 1/r+1/s may or may not be =4 thus insufficient
so Answer is A



Director
Joined: 12 Jun 2006
Posts: 532

Re: DS: 246 [#permalink]
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11 Jun 2007, 23:36
ywilfred wrote: bkk145 wrote: ggarr wrote: if rs is not equal to 0, is 1/r + 1/s = 4?
1) r+s = 4rs 2) r = s
Please explain your solution The answer is A. 1) (r+s) / rs = 4 => (r/rs) + (s/rs) = 4 => (1/r) + (1/s) = 4 SUFFICIENT2) plug in r=s=1/2, you get 4=4. But plug in r=s=1, you get 2=4. INSUFFICIENT. gar!! failed to see that... why can't we just answer this question w/the info provided in the stem? did we really need additional info to figure that out? 1/r + 1/s = 4 => s/rs + r/rs = 4 => 1/r + 1/s = 4
does this make sense?



Manager
Joined: 17 Oct 2006
Posts: 52

Well we could certainly have done it that way Fig if the stem had told us that 1/r+1/s is indeed equal to 4. The stem is asking whether the expression is a true equation or not. And to validate the stem we are provided with two different sets of information which are statements A & B.
Actually this is how i had made D the correct option by putting r=s in the stem. But as u see, stem is not stated to be true, it is asked wherther it is true or not.
I hope this explains ur question.



Director
Joined: 12 Jun 2006
Posts: 532

it does. thanks. I made this more difficult than I should have. why are you calling me Fig?



Manager
Joined: 17 Oct 2006
Posts: 52

sorry dude
u see when the boss is just around the corner, then such mistakes are bound to happen. Especially when ur boss is more like a blood hound, who only wnats ur blood instead of ur sweat.
And yes u did make it more difficult. It happens to me too. simple solution is in fornt of me, but i start making complex equations.



SVP
Joined: 01 May 2006
Posts: 1796

ggarr wrote: it does. thanks. I made this more difficult than I should have. why are you calling me Fig?
Because I'm the one who will do such thing
By the way, I'm also with (A) ...... because neither r nor s could be equal to 0..... We can thus divide the equation by rs.



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Schools: Chicago Booth Class of 2010

Re: DS: 246 [#permalink]
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12 Jun 2007, 02:18
ggarr wrote: if rs is not equal to 0, is 1/r + 1/s = 4?
1) r+s = 4rs 2) r = s
Please explain your solution
From the stem we have that (r+s)/rs = 4
1) (r+s)/rs= 4rs/rs = 4, SUF
2) r=s, from the stem => 1/r, but since we do not know how much does r worth we also do not know how much 1/r worths, INSUF.
A



Manager
Joined: 04 Jan 2014
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Re: if rs is not equal to 0, is 1/r + 1/s = 4? 1) r+s = 4rs 2) r [#permalink]
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22 Feb 2014, 22:19
why is (1) sufficient? if r = 0.3 and s = 0.2, 4rs = 0.24. s+r = 0.5. The question didn't state that r and s are integers.



Intern
Joined: 03 Jul 2013
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Re: if rs is not equal to 0, is 1/r + 1/s = 4? 1) r+s = 4rs 2) r [#permalink]
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22 Feb 2014, 23:43
r+s=4 rs or (r+s)/rs=4 or (r/rs)+(s/rs)=4 or 1/r+1/s=4 . so sufficient .
statements 2 is clearly out . correct answer = A .
if this portion of the question " rs is not equal to 0 " is not given , then ? what would happen ?
Posted from my mobile device



Math Expert
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Posts: 39713

Re: if rs is not equal to 0, is 1/r + 1/s = 4? 1) r+s = 4rs 2) r [#permalink]
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23 Feb 2014, 02:32
shiblee wrote: r+s=4 rs or (r+s)/rs=4 or (r/rs)+(s/rs)=4 or 1/r+1/s=4 . so sufficient .
statements 2 is clearly out . correct answer = A .
if this portion of the question " rs is not equal to 0 " is not given , then ? what would happen ?
Posted from my mobile device If rs#0, is 1/r + 1/s = 4 ?Question: is \(\frac{1}{r}+\frac{1}{s}=4\) > is \(\frac{r+s}{rs}=4\) > is \(r+s=4rs\)? (1) \(r+s=4rs\), directly answers the question. Sufficient. (2) \(r = s\), the question becomes: is \(\frac{1}{r}+\frac{1}{r}=4\) ? > is \(r=\frac{1}{2}\)? but we dont' know whether \(r=\frac{1}{2}\). Not sufficient. Answer: A. As for your question: if rs#0 were not given, then r=s=0 would be possible and in this case 1/r + 1/s would be undefined. OPEN DISCUSSION OF THIS QUESTION IS HERE: http://gmatclub.com/forum/ifrs0is1 ... 02597.html
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Re: if rs is not equal to 0, is 1/r + 1/s = 4? 1) r+s = 4rs 2) r
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23 Feb 2014, 02:32







