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If rs <> 0 , is 1/r + 1/s = 4? r + s = 4rs r = s

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If rs <> 0 , is 1/r + 1/s = 4? r + s = 4rs r = s [#permalink] New post 10 Oct 2010, 05:29
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If rs <> 0, is \frac{1}{r} + \frac{1}{s} = 4?

    r + s = 4rs
    r = s

Please note that <> in the question should be read as "Not Equal To".

[Reveal] Spoiler: OA and my Assumption
OA is "A". That's only A is sufficient. but I presume that that answer should be "C" because for me r=s , if I substitute in the equation then

1/r + 1/r = 2/r = 4
r = 1/2 and I am able to prove the condition. Although, OG has taken values of r and s to prove that 2nd condition is not sufficient, then why not try to put some values for r and s in the 1st option too?
Please help
[Reveal] Spoiler: OA

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Re: OG 10 Qn: 246 [#permalink] New post 10 Oct 2010, 05:38
zerotoinfinite2006 wrote:
If rs <> 0, is \frac{1}{r} + \frac{1}{s} = 4?

    r + s = 4rs
    r = s

Please note that <> in the question should be read as "Not Equal To".

[Reveal] Spoiler: OA and my Assumption
OA is "A". That's only A is sufficient. but I presume that that answer should be "C" because for me r=s , if I substitute in the equation then

1/r + 1/r = 2/r = 4
r = 1/2 and I am able to prove the condition. Although, OG has taken values of r and s to prove that 2nd condition is not sufficient, then why not try to put some values for r and s in the 1st option too?
Please help


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.
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Need help with DS [#permalink] New post 30 Nov 2010, 11:08
Q. r,s not equal to zero. Is 1/r + 1/s = 4 ?

(1) r + s = 4rs
(2) r = s

I have always had a doubt on when to solve intuitively and when to solve algebrically. Can some please clarify this doubt. Thanks
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Re: Need help with DS [#permalink] New post 30 Nov 2010, 11:15
ajit257 wrote:
Q. r,s not equal to zero. Is 1/r + 1/s = 4 ?

(1) r + s = 4rs
(2) r = s

I have always had a doubt on when to solve intuitively and when to solve algebrically. Can some please clarify this doubt. Thanks


Merging similar topics.

As for your doubt I'd suggest algebraic way for this one.
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DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set. NEW!!!


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Re: OG 10 Qn: 246 [#permalink] New post 30 Nov 2010, 11:24
Hi
if i go the algebric way on statement 1 i get it right but statement 2 i get it wrong so I am kinda confused
eg statement 2 sates r = s

so lets see 1/r + 1/s = 4
can be written as r + s = 4 rs
so replacing r we get 2s = 4s^2
s = 1/2
so statement 2 is also sufficient hence ans is D but this is not correct
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Re: OG 10 Qn: 246   [#permalink] 30 Nov 2010, 11:24
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