manhatan gmat ds

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manhatan gmat ds

by resilient » Mon Feb 11, 2008 10:07 pm
Is absolute value A + abslute value B > ABSOLUTE VALUE a+B?

1. a^2 > b^2
2. Absolute value a * b < 0

I chose d but answer to my slap in the face was E
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by sankruth » Tue Feb 12, 2008 2:02 am
Please confirm if I have got the question right...

Is Abs(A) + Abs(B) > Abs(A + B)?

The only cases this is possible are when A and B have different signs. If A & B have the same sign both sides of the equation will be equal.

St 1

A^2 > B^2

This statement reveals nothing about the sign of A & B. In other words all possible combinations of +ve and +ve numbers for A & B will satisfy St 1. So INSUFF, leaves us with B, C & E

St 2

Abs(A) * B < 0

So, B is -ve. But A could be both +Ve and -ve So INSUFF, leaves us with C & E

Taking 1 & 2 together, we still cannot determine the sign for A. So E

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by maihuna » Tue Apr 14, 2009 7:55 am
i got this question almost wrong. as I assumed a to be +ive (my fault)... Ian do u have a better soln? I prefer algebriac one..?

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by mike22629 » Tue Apr 14, 2009 8:39 am
The best way to approach these problems is by using a number line and to think.

Basically you need to find out the signs of A and B. This is because if they are on opposite sides of the number line, the lAl + lBl will always = lA+Bl

If they are on the same side, lAl + lBl always > lA+Bl

1) Does not tell you about signs. Insignificant
2) Tells you B is negative, but does not tell you about A's sign

IMO E.
Just practice using number lines and these problems will get a lot easier.

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by vittalgmat » Thu Apr 16, 2009 12:51 pm
mike22629 wrote:The best way to approach these problems is by using a number line and to think.

Basically you need to find out the signs of A and B. This is because if they are on opposite sides of the number line, the lAl + lBl will always = lA+Bl

If they are on the same side, lAl + lBl always > lA+Bl

1) Does not tell you about signs. Insignificant
2) Tells you B is negative, but does not tell you about A's sign

IMO E.
Just practice using number lines and these problems will get a lot easier.
Mike mentioned an important takeaway
I have highlighted it.

Thanks Mike.

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