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papumba2011
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A baffling problem
This topic has expert replies
Source: Beat The GMAT — Data Sufficiency |
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thephoenix
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papumba2011
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Yes. Can you explain the answer a bit. I actually want to know the process by which you aarrive at the value using stmt 1.thephoenix wrote:IS the ans D
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neoreaves
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to simplify the first expression lets say z = x- 5
then sqrt(z^2) = -z
the LHS is definitely positive as we are squaring z and then taking a sqrt of it ....so in ths process if it is a negative number we will get a positive and if it is a positive number then we get the same positive number
so LHS serves as a modulus operator similar to |z| ...
however, notice that RHS is -z ....this indicates one thing and that is z < 0 ...thus a -z is a positive number ..
Thus from all this what we are getting at is z < 0 which in our case is x - 5 < 0 --> x < 5 ??
That is what we have to find out
1) x < 0 .........so our answer to x < 5 is here ....yes it is less than 5 !! ...so Sufficient
2) 5 -x > 0
5 > x
or x < 5 .....again answers our questions ...so Sufficient
then sqrt(z^2) = -z
the LHS is definitely positive as we are squaring z and then taking a sqrt of it ....so in ths process if it is a negative number we will get a positive and if it is a positive number then we get the same positive number
so LHS serves as a modulus operator similar to |z| ...
however, notice that RHS is -z ....this indicates one thing and that is z < 0 ...thus a -z is a positive number ..
Thus from all this what we are getting at is z < 0 which in our case is x - 5 < 0 --> x < 5 ??
That is what we have to find out
1) x < 0 .........so our answer to x < 5 is here ....yes it is less than 5 !! ...so Sufficient
2) 5 -x > 0
5 > x
or x < 5 .....again answers our questions ...so Sufficient
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neoreaves
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dxgamez wrote:@neoreaves
Can we also multiply the powers of (x-5) or z in your expression?
{(z)^2}^1/2 = z ?
Can we do this? Or rather when should we simplify the expression?
Yes we can do this. But I think that is not the point here .....GMAT inequalities are nothing like the inequalities you or I have encountered in real life ....we have to make sense of what the equality is saying ....so look at the broader picture ...even if you cancel out the powers you get z ...but the RHS is -z ...Why is this ??.....the only possibility is z < 0 .....so all this mumbo jumbo is created by GMAT so you can arrive at this conclusion ...that z < 0 .....try to read the inequality what is it saying .....simplifying an equality is not wrong ...but interpretting it is GOLD .....take a few numbers play with this inequality ....i know it took me quiet some time to get comfortable with this but I am sure you can do better than me
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harshavardhanc
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sqrt of ( (x-5)^2) can bepapumba2011 wrote:Is{ (x-5)^(2)}^(1/2) = 5-x
1) -x|x| > 0
2) 5-x > 0
+(x-5) or -(x-5)
the question is asking if it is the second one.
The root will be -(x-5) when x-5 < 0 or X<5.
statement 1 : gives us x<0 . Sufficient.
statement 2 : directly gives us x<5. sufficient.
Hence , D.
Regards,
Harsha
Harsha
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gmatmachoman
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Guys this is my way of reasoning. Plz do ch\k out if I am wrong !papumba2011 wrote:Is{ (x-5)^(2)}^(1/2) = 5-x
1) -x|x| > 0
2) 5-x > 0
It asks for whether (x-5) = (5-x)
St1 :
-x|x| > 0
In this case, x has to be negative number (x<0)
Plugging in some values of x (X<0) ,LHS is NOT equal to RHS.( Sufficient)
St 2: 5-x > 0---> x<5
Pluggng in values of X in the query we get LHS is NOT equal to RHS ( Sufficient)
IMO D.
Plz share ur view am i correct!!
st 2:
