Gmat prep question pack

[ankitdhingra007]

hey guys,

This question is from GMAT prep question pack 1:

Is x positive?
1. 1/(x+1) < 1
2. (x-1) is a perfect square

According to me the ans should be D - both statements are sufficient. However, official answer is B.

Experts' thoughts??

[jnelson0612]

hey guys,

This question is from GMAT prep question pack 1:

Is x positive?
1. 1/(x+1) < 1
2. (x-1) is a perfect square

According to me the ans should be D - both statements are sufficient. However, official answer is B.

Experts' thoughts??

Sure! This is an ideal situation in which to test numbers because you have a yes/no data sufficiency question involving variables.

Let's test numbers in statement 1 and show why it is insufficient.

Okay, we have no constraints for x. Let's just pick an x that makes 1/(x+1) < 1 true.
If x=2, then 1/3 < 1 is true. x can be 2.
Is x positive? YES

Now, let's pick another x that makes our statement true but that provides us with a different answer to the question in the stem:
If x=-2, then 1/(-1) < 1 is true. x can be -2.
Is x positive? NO

Once I have answered the question YES and NO, I have proved that the statement is insufficient. A and D are not viable answer choices.

Please let me know if you have any confusion or wish to discuss this any further. :-)

[ankitdhingra007]

Thanks so much Jamie for the explanation. However, one small clarification.. Cant we solve the equation 1/(x+1) < 1 in following way:

If i multiply with (x+1) on both sides, i have:

1<(x+1) which then leads me to x>0 and hence is positive. Or am i missing something here?

Thanks again for your time! :)

[tim]

you can't multiply both sides by x+1 unless you know beforehand that x is positive..

[ankitdhingra007]

Sounds valid.. realiZed my error.. thanks so much guys..

[RonPurewal]

Sounds valid.. realiZed my error.. thanks so much guys..

excellent.
make sure, though, that you also learn the method of testing cases (used by jamie above) very thoroughly. ideally, case-testing should have just as high a priority in your mind as algebra.

[ankitdhingra007]

To begin with, please accept my sincere respect for the entire MGMAT team.. Ron, Jamie, and Stacey and all the other staff who makes this forum and company a great success.. Specially the inputs (apart from course stuff) you guys offer is awesome..

I took my GMAT last Wednesday and scored 690 and i now have a couple of questions -

1. I plan to apply for PhD programs in schools like Rotman, Sauder, Schulich, Richard Ivey, Warwick etc.
2. I am already and MBA with a GPA of 3.2 and i have a work ex of 4 years..

Could you guys please throw in some light as to what prospects do i have (if any need to retake the GMAT) etc? Because when i browse through the website of these schools it asks for GMAT> 600..

[jnelson0612]

To begin with, please accept my sincere respect for the entire MGMAT team.. Ron, Jamie, and Stacey and all the other staff who makes this forum and company a great success.. Specially the inputs (apart from course stuff) you guys offer is awesome..

I took my GMAT last Wednesday and scored 690 and i now have a couple of questions -

1. I plan to apply for PhD programs in schools like Rotman, Sauder, Schulich, Richard Ivey, Warwick etc.
2. I am already and MBA with a GPA of 3.2 and i have a work ex of 4 years..

Could you guys please throw in some light as to what prospects do i have (if any need to retake the GMAT) etc? Because when i browse through the website of these schools it asks for GMAT> 600..

Thank you for your kind words! I speak for all of us when I say that we really enjoying interacting with students here.

Your question is outside our area of expertise but I can recommend a great company to speak with, MBAmission (www.mbamission.com). They are a sister company (we refer back and forth) and we have great confidence in the advice they provide. Go to their website and request a free 30 minute consultation; in this consultation you can ask this question. I would believe and trust in anything their people have to say. Best wishes!

[ankitdhingra007]

thanks Jamie.. but will they provide guidance/consultation for a PhD applicant??

Thanks!

[jnelson0612]

thanks Jamie.. but will they provide guidance/consultation for a PhD applicant??

Thanks!

Very possibly! You may want to call and ask about that, and if they say yes then schedule the 30 minute consultation.