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If P + |k| > |P| + k then which of the following is true of Inqual

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Re: If P + |k| > |P| + k then which of the following is true of Inqual  [#permalink]

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New post 29 Oct 2016, 20:43
sunny3011 wrote:
If P + |k| > |P| + k then which of the following is true of Inequalities ?

A. P=K
B. P<=k
C. P<k
D. P>k
E. Can't determined

Again strucked with Inequalities ? Need Help.

Bunuel and VeritasPrepKarishma ?



P + |k| > |P| + k


Square both sides


P^2 + k^2 +2*P*|k| > P^2 + k^2 + 2*|P|*k

P*|k| > |P|*k

P/|P| > k/|k|

We all know that x/|x| can be 1 or -1.

So in the above inequality LHS will be +1 and RHS will be -1.

Which means P is positive and k is negative.

P>k

D


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If P + |k| > |P| + k then which of the following is true of Inqual  [#permalink]

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New post 30 Nov 2016, 04:01
akumar5 wrote:
given that P + |k| > |P| + k.................1

lets square both sides : p^2+k^2+2p|k| > p^2+k^2+2k|p|

so, p|k|>k|p| ;
Clearly, the above statement is valid only if p>k

Answer is D


I like your answer, but can you really square both sides of inequality when you dont know whether either side is +ve or -ve?
I've heard you shouldnt, if you don't know
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Re: If P + |k| > |P| + k then which of the following is true of Inqual  [#permalink]

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New post 30 Nov 2016, 18:55
Krage17 wrote:
I am neither of two you asked to help, but I am retaking the GMAT soon, so here is how I approached this problem:

Assuming that P and k and both sides have the absolute value, the only way we will have an inequality is when when one or more numbers have negative signs, and thus change their value when an absolute value is taken. We already know that P on the left side equals |P| on the right side because the left side of the inequality is larger (and therefore, there is no way P is negative). So, what truly shifts the equation here is the sign flip when we take an absolute value of k. In other words, k must be negative, otherwise |k| would be equal to k and P+|k| would be equal to |P|+k. Hence, P (which is positive) must be larger than k (which is negative).
I know it's somewhat conceptual and may not be easy to follow, but that's how I looked at it.


This approach is interesting, and i think the most efficient way to approach this problem. But your assumption here is wrong my friend-

Here's how P can be negative:
p = -1, k = -2
p + |k| > |p| + k
-1 + |-2| > |-1| + (-2)
1 > -1

This is true for any negative value of p when k<p.

So we cannot conclude that p is non-negative. However, what we can certainly conclude from the given inequality is- k has to be negitive

|Any number| \(\geq\) That number

Now, the given inequality:
p + |k| > |p| + k
The |k| on LHS can be greater than or equal to k on RHS

Case 1:
|k| = k, which means that k is positive
in this case, to hold the ineq. true p > |p|. But this cant be true. Hence K is negative.

Case 2:
|k| > k, which means that k is negative
in this case, to hold the ineq. true, p on the LHS can be equal to (p is positive) or less than (p is negative) |p| on RHS.

So we can safely conclude from the given ineq. that
p can be +ve or -ve, but
k will always be -ve

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Re: If P + |k| > |P| + k then which of the following is true of Inqual  [#permalink]

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New post 06 Dec 2017, 13:18
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Re: If P + |k| > |P| + k then which of the following is true of Inqual &nbs [#permalink] 06 Dec 2017, 13:18

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