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Is xm < ym ?

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Is xm < ym ? [#permalink]

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New post 26 Jul 2017, 09:10
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C
D
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Question Stats:

72% (00:41) correct 28% (00:40) wrong based on 330 sessions

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Re: Is xm < ym ? [#permalink]

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New post 13 Aug 2017, 08:42
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carcass wrote:
Is \(xm < ym\) ?

(1) \(x > y\)

(2) \(m < 0\)


Target question: Is xm < ym?
Another approach is to rephrase the target question.

Take the inequality and subtract ym from both sides to get: xm - ym < 0
Factor out the m to get m(x - y) < 0
In other words....
REPHRASED target question: Is m(x - y) a NEGATIVE value?

Statement 1: x > y
Subtract y from both sides to get: x - y > 0
So, x - y is a POSITIVE value
Does this provide enough information to determine whether or not m(x - y) a NEGATIVE value?
No. We still don't know anything about the value of m
Since we cannot answer the REPHRASED target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: m < 0
In other words, m is NEGATIVE
Does this provide enough information to determine whether or not m(x - y) a NEGATIVE value?
No. We don't know anything about the value of (x - y)
Since we cannot answer the REPHRASED target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 1 tells us that x - y is a POSITIVE value
Statement 2 tells us that m is a NEGATIVE value
So, m(x - y) = (NEGATIVE)(POSITIVE) = some NEGATIVE VALUE
In other words, m(x - y) is definitely a NEGATIVE value
Since we can answer the REPHRASED target question with certainty, the combined statements are SUFFICIENT

Answer:

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Re: Is xm < ym ? [#permalink]

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New post 26 Jul 2017, 09:20
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1
Using both statements, if we take the inequality in Statement 1:

x > y

and multiply by m on both sides, we need to reverse the inequality, because, as Statement 2 tells us, m < 0. So we get

xm < ym

which is what we wanted. Statement 1 is not sufficient alone because we need to know if m is positive or negative, and Statement 2 is not sufficient alone since we have no information about x or y. So the answer is C.
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Re: Is xm < ym ? [#permalink]

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New post 03 Aug 2017, 09:06
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carcass wrote:
Is \(xm < ym\) ?

(1) \(x > y\)

(2) \(m < 0\)


this is more simple method

xm<ym
move ym to the left
xm-ym<0
m(x-y)<0

now we can analyse , applying case 1 and 2.
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Re: Is xm < ym ? [#permalink]

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New post 13 Aug 2017, 03:29
Hi,

m(x-y)<0 -- > m<0 or x>y
do we need 2 conditions together or each condition alone is suff??

as it is m<0 OR x>y can we not select D as the answer?
please clarify.

Thanks. :)
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Re: Is xm < ym ? [#permalink]

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New post 02 May 2018, 21:29
1
GMATPrepNow wrote:
carcass wrote:
Is \(xm < ym\) ?

(1) \(x > y\)

(2) \(m < 0\)


Target question: Is xm < ym?
Another approach is to rephrase the target question.

Take the inequality and subtract ym from both sides to get: xm - ym < 0
Factor out the m to get m(x - y) < 0
In other words....
REPHRASED target question: Is m(x - y) a NEGATIVE value?

Statement 1: x > y
Subtract y from both sides to get: x - y > 0
So, x - y is a POSITIVE value
Does this provide enough information to determine whether or not m(x - y) a NEGATIVE value?
No. We still don't know anything about the value of m
Since we cannot answer the REPHRASED target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: m < 0
In other words, m is NEGATIVE
Does this provide enough information to determine whether or not m(x - y) a NEGATIVE value?
No. We don't know anything about the value of (x - y)
Since we cannot answer the REPHRASED target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 1 tells us that x - y is a POSITIVE value
Statement 2 tells us that m is a NEGATIVE value
So, m(x - y) = (NEGATIVE)(POSITIVE) = some NEGATIVE VALUE
In other words, m(x - y) is definitely a NEGATIVE value
Since we can answer the REPHRASED target question with certainty, the combined statements are SUFFICIENT

Answer:

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In this case, we can subtract ym from both sides even though we don't know their signs?
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Re: Is xm < ym ? [#permalink]

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New post 02 May 2018, 23:45
thinkpad18 wrote:
In this case, we can subtract ym from both sides even though we don't know their signs?


We are concerned about the sign of a variable when multiplying/dividing an inequality by it. However we can safely add/subtract a variable from both sides of an inequality regardless of its sign.

9. Inequalities




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Re: Is xm < ym ? [#permalink]

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New post 03 May 2018, 07:01
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thinkpad18 wrote:
In this case, we can subtract ym from both sides even though we don't know their signs?


When it comes to solving inequalities, we can safely add or subtract ANY value from both sides, and the resulting inequality will be perfectly valid.
However, if we multiply or divide both sides by a NEGATIVE value, then we must REVERSE the direction of the inequality symbol.

More here:

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Re: Is xm < ym ? [#permalink]

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New post 28 May 2018, 09:51
Hi!! Is this approach correct?

xm<ym
xm-ym<0
m(x-y)<0
is m<0 and x<y?

1. x>y but does not tell us the value of m hence not sufficient

2. M>0 but does not tell us for x or y hence not sufficent.

Combining 1+2, we get x>y and M>0 hence a definite yes.

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Re: Is xm < ym ? [#permalink]

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New post 07 Jun 2018, 19:48
asfandabid wrote:
Hi!! Is this approach correct?

xm<ym
xm-ym<0
m(x-y)<0
is m<0 and x<y?

1. x>y but does not tell us the value of m hence not sufficient

2. M>0 but does not tell us for x or y hence not sufficent.

Combining 1+2, we get x>y and M>0 hence a definite yes.

Bunuel
VeritasPrepKarishma


Evaluate this properly: m(x-y)<0
This means the product of m and (x - y) is negative. So, either m is positive and (x - y) negative OR m is negative and (x - y) positive.
The two statements together tell us hat (x - y) is positive and m is positive.

So we know for sure that m(x-y) is positive. Sufficient.
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Re: Is xm < ym ?   [#permalink] 07 Jun 2018, 19:48
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