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kindly solve it by giving explanation.......

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by testcircle » Mon Dec 28, 2009 12:21 am
If a+b = 12, and 1/a + 1/b= 6, then what should be the value of ab


(A) 1/2
(B) -3
(C) 2
(D) -2
(E) 1/6

I have seen this problem on www.TC.com/GRE, in sample questions. kindly solve it by an another method

Looking for a good reply.
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by Alfred » Mon Dec 28, 2009 12:41 am
good question[/list]
Last edited by Alfred on Mon Mar 22, 2010 11:47 pm, edited 1 time in total.
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by heshamelaziry » Mon Dec 28, 2009 1:05 am
IMO C
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by thephoenix » Tue Dec 29, 2009 5:56 am
1/a + 1/b=(b+a)/ab=6----->ab=(a+b)/6=12/6=2
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by Alfred » Mon Mar 22, 2010 11:55 pm
Look,
1/a + 1/b = (a+b)/2
(b+a)/ab = (a+b)/2
simply, ab = 2

if i talk about my opinion then according to me you should to visit to that particular site where from you found this question, because i have also seen these type problem on https://www.TestCircle.com/GMAT FREE SAMPLE VIDEOS, and i found that it was described in a simple and understanding way.
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by Phirozz » Tue Mar 23, 2010 12:23 am
Mod !!

Could u plz shift this question to QA thread
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by reply2spg » Tue Mar 23, 2010 8:14 am
Answer is C. however, this question should be in quant section.

ok here is the solution.

(1/a) +(1/b) = 6
Find out the LCM of both fractions. it is 'ab'. multiply by 'b' to first term and by 'a' to second term. final result will be

[(a+b)/ab] = 6.

We know that a+b =12. replace a+b with 12 in the equation.

[12/ab] = 6. Move 'ab' to right hand side and '6' to left hand side.

(12/6) = ab. Therefore, ab = 2 (C)
testcircle wrote:If a+b = 12, and 1/a + 1/b= 6, then what should be the value of ab


(A) 1/2
(B) -3
(C) 2
(D) -2
(E) 1/6

I have seen this problem on www.TC.com/GRE, in sample questions. kindly solve it by an another method

Looking for a good reply.
[/b]
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