Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 25 May 2013, 09:29

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

Author Message
TAGS:
Manager
Joined: 17 Aug 2010
Posts: 54
Followers: 0

Kudos [?]: 3 [0], given: 18

If rs <> 0 , is 1/r + 1/s = 4? r + s = 4rs r = s [#permalink]  10 Oct 2010, 05:29
00:00

Question Stats:

68% (01:41) correct 31% (01:17) wrong based on 1 sessions
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?
[Reveal] Spoiler: OA

_________________

I don't want kudos.. I want to see smile on your face if I am able to help you.. which is priceless.

GMAT Club team member
Joined: 02 Sep 2009
Posts: 11633
Followers: 1802

Kudos [?]: 9611 [0], given: 829

Re: OG 10 Qn: 246 [#permalink]  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?

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.

_________________
Senior Manager
Joined: 28 Aug 2010
Posts: 280
Followers: 3

Kudos [?]: 20 [0], given: 11

Need help with DS [#permalink]  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
_________________

Gmat: everything-you-need-to-prepare-for-the-gmat-revised-77983.html
-------------------------------------------------------------------------------------------------
Ajit

GMAT Club team member
Joined: 02 Sep 2009
Posts: 11633
Followers: 1802

Kudos [?]: 9611 [0], given: 829

Re: Need help with DS [#permalink]  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.
_________________
Senior Manager
Joined: 28 Aug 2010
Posts: 280
Followers: 3

Kudos [?]: 20 [0], given: 11

Re: OG 10 Qn: 246 [#permalink]  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
_________________

Gmat: everything-you-need-to-prepare-for-the-gmat-revised-77983.html
-------------------------------------------------------------------------------------------------
Ajit

Re: OG 10 Qn: 246   [#permalink] 30 Nov 2010, 11:24
Similar topics Replies Last post
Similar
Topics:
If r+s=4, is 0>s? 1, r>4 2, 4>s 3 22 Sep 2005, 04:56
If r>0 and s>0, is r/s < s/r? (1) r/3s = 1/4 (2) s= 8 14 Oct 2005, 11:53
if rs is not equal to 0, is 1/r + 1/s = 4? 1) r+s = 4rs 2) r 12 11 Jun 2007, 22:19
1 Is r > s ? (1) -r + s < 0 (2) r < | s | 2 01 Oct 2010, 08:58
1 If rs 0, does 1/r + 1/s = 1 (1) rs = 1 (2) s + r = 2.5 Did 4 12 Dec 2010, 09:05
Display posts from previous: Sort by