Absolute value

[beater]

Is m < 0?

1. -m = |-m|
2. m^2 = 9

[Ian Stewart]

Is m < 0?

1. -m = |-m|
2. m^2 = 9

A bit of a tricky one, because one exception makes the first statement insufficient. Notice that, in the equation in statement 1, the right side of the equation can't be negative. That means, looking at the left side, that m can't be positive. m can certainly be negative, but 1 is still insufficient: m might be equal to zero. Statement 2 is clearly insufficient, but together, m must be -3. C.

[beater]

Ian - could you please explain as to how you concluded M = NEGATIVE from statement 1.

[cramya]

Stmt I

-m = |-m|

LetS say m was positive let m=2

-m = -2

|-m| = |-2| = 2

-2 can never equal 2 or in fact no positive values work. Therefore x has to be negative or non positive(0 like Ian said)

For eg: x= -2

-m = -(-2) = 2

|-m| = |- (-2)| = 2

-0,+0,0 everything the same (STMT I WILL WORK FOR 0 ALSO)

INSUFF

Stmt II

m^2 = 9

|m| = 3

m=3 or -3

INSUFF

Together like Ian said m has to be -3 therefore m<0

Choose C)

Regards,
CR

[logitech]

Is m < 0?

Let's star with the easy statement:


2. m^2 = 9[/quote]

This gives is m is either 3 or -3

( since the statements never contradict in GMAT we know that we should be testing the first statement for these two numbers but BE VERY CAREFUL. This piece of info can lead you to carry information over. SO KNOW THIS but FORGET IT!

1. -m = |-m|

m=0 fits the bill here

m < 0 ( let's say -3 )

-(-3) = |-(-3)|

3 = 3

m > 0 (lets say 3)

- 3 = 3

Well we actually did not need to carry the calculation all the way here because the absolute value is always a positive number so here we have two solution

m < 0 Which is most of the people would find out and which will lead people to choose A

AND

m = 0 Which is the sneaky bastard whom we should keep an eye on DS questions.

Statement 1 & 2

together we know that - 3 is the guy we are looking for!

Choose C

[Ian Stewart]

Ian - could you please explain as to how you concluded M = NEGATIVE from statement 1.

I concluded that m was either negative or 0 from statement 1. I can try to explain in a different way, though as was done above, it's perhaps easier to see by plugging in a negative and a positive number for m to see what happens.

We know that:

1. -m = |-m|

The right side is an absolute value, so can never be negative. If the right side of the equation isn't negative, the left side can't be negative either. Now, -m can't be negative; if m were positive, -m will be negative, so m can't be positive. m can be zero or negative.

[malhotneha]

Is m < 0?

Let's star with the easy statement:


2. m^2 = 9

This gives is m is either 3 or -3

( since the statements never contradict in GMAT we know that we should be testing the first statement for these two numbers but BE VERY CAREFUL. This piece of info can lead you to carry information over. SO KNOW THIS but FORGET IT!

1. -m = |-m|

m=0 fits the bill here

m < 0 ( let's say -3 )

-(-3) = |-(-3)|

3 = 3

m > 0 (lets say 3)

- 3 = 3

Well we actually did not need to carry the calculation all the way here because the absolute value is always a positive number so here we have two solution

m < 0 Which is most of the people would find out and which will lead people to choose A

AND

m = 0 Which is the sneaky bastard whom we should keep an eye on DS questions.

Statement 1 & 2

together we know that - 3 is the guy we are looking for!

Choose C[/quote]

Quickly Logitech, why is m=0? Its not given in the question thread? I initially chose A.
I am definitely overlooking sth...please explain.

[logitech]

Quickly Logitech, why is m=0? Its not given in the question thread? I initially chose A.
I am definitely overlooking sth...please explain.

Well we found that m could be also 0. This was why we could not choose A.

[malhotneha]

Quickly Logitech, why is m=0? Its not given in the question thread? I initially chose A.
I am definitely overlooking sth...please explain.

Well we found that m could be also 0. This was why we could not choose A.

Thanks, I got this one....Cheers