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Logarithm

by john123 » Sun Jan 08, 2012 5:16 am
What is the maximum value of log(x)[x/y]+log(y)[y/x] {log(x)[x/y] ==> logarithm of [x/y] to base x}
Given, x>=y and y>1.
  • a) -1
    b) -0.5
    c) 0
    d) 1
    e) no of these
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by sam2304 » Sun Jan 08, 2012 7:23 am
I don't think GMAT tests logarithms. Please post GMAT related questions and don't waste your precious time as well preparing unnecessary topics which are not covered by GMAT.
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by ronnie1985 » Mon Jan 09, 2012 3:14 am
This can be done by base change formula and property of logarithms. The explanation is attached.
(C) is answer.
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The Logarithm
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by ronnie1985 » Sat Jan 14, 2012 9:55 am
I am sorry John, it was a error on my behalf to write in this fashion: -[...]. There is no negative sign outside. So the answer will be negative for any value of x and y which are not equal to each other, making zero the maximum possible value of the expression.
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by ronnie1985 » Sat Jan 14, 2012 10:26 am
The attachment is edited for your reference.
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by avik.ch » Sun Jan 15, 2012 10:11 pm
john123 wrote:What is the maximum value of log(x)[x/y]+log(y)[y/x] {log(x)[x/y] ==> logarithm of [x/y] to base x}
Given, x>=y and y>1.
  • a) -1
    b) -0.5
    c) 0
    d) 1
    e) no of these
What is the source of this question ?

GMAT will never give you this question. I couldnt find any in OG.
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