GMatPrep-DS : GMAT Data Sufficiency (DS)

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GMatPrep-DS [#permalink]

09 Sep 2007, 08:31

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Can some please explain this.

From 1) the inequality becomes is r^2 + 2 > r^2, regardless of r being postive or negative or 0, the ineqiality holds good.

From 2) it does not say anything about p.

please explain why the answer is not A.

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09 Sep 2007, 08:39

Just plug in the numbers once negative than positive, you will see that they are siffices together

Ans: C

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Re: GMatPrep-DS [#permalink]

16 Sep 2007, 11:06

zion wrote:

Ans can not be A.

Let's take r = 0 then as per ST1 p=r
So (1/p) = (1/0) which is not defined.

If we combine ST1 and ST2,
Then "r" should be greater than 0 and in this case, 1/P will always be greater than r/(r^2+2).
You can verify this by putting any value of r >0.

Hence C.

- Brajesh

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16 Sep 2007, 12:20

Ferihere wrote:

Just plug in the numbers once negative than positive, you will see that they are siffices together

Ans: C

I am not sure if thats the correct way. Even if you substiute once -ve and one +ve number , you should still get A .
I think brajesh is correct that we need to consider the number 0 here.

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16 Sep 2007, 13:19

1/p > r/(r^2+2) ---> true ?

statement 1

p = r

1/p > p/(p^2+2)

1 > p^2/(p^2+2) ---> if p>0

p^2+2 > p^2

2 > 0 ---> true

1 < p^2/(p^2+2) ---> if p<0

Note ! if you double by p to get this outcome you have doubled by a negative number ! to get p^2 you need to flip signs !!

p^2+2 < P^2

2 < 0 ---> false

insufficent

statement 2

r > 0

insufficent

both statements

since r = p

1/p > p/(p^2+2)

1 > p^2/(p^2+2) ---> if p>0 ---> given

p^2+2 > p^2

2 > 0 ---> true

sufficient

the answer is (C)

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16 Sep 2007, 23:15

St1:
If p = r = 2,
1/2 > 2/6 ? --> yes.

If p = r = -2
-1/2 > -2/6 --> No.

Insufficient.

St2:
Nothing about p. insufficient.

St1 & St2:
If p = r = 2,
1/2 > 2/6? --> yes.

If p = r = 1/2
2 > 2/9? --> yes.

Sufficient.

Ans C

[#permalink] 16 Sep 2007, 23:15

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