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Re: OG DS 95, explain how my logic is wrong [#permalink]
14 Feb 2010, 10:34

2

This post received KUDOS

Currency wrote:

Ok, without a doubt my number property skills are my achillies heel when is comes to GMAT quant.

I was reviewing my error log today. Tell me why my logic is wrong.

95. Is rst=1

(1) rs=1 (2) st=1

I attacked it by rearranging the original equations, dividing both sides by t.

so, rs=1/t then sub in rs=1 so, 1=1/t then cross multiply t=1 Combined with what we already know (rs=1) we have 1*1=1 Therefore, sufficient.

Same logic can be applied to statment 2. Therefore my answer was D.

OA is actually E and I understand how they got it, but I also fail to see why my strategy was wrong. I feel like I'm probably overlooking some basic rule that governs all equations here but if someone could help me out that'd be great.

Thanks

The highlighted part is the mistake.

The question is asking u to prove that... and you are considering the same as True. This isnt the correct approach.

The Answer E is correct...

Is rst = 1? S1: rs = 1, t can be 2 ... then rst is not equal to 1... t can be 1... then rst is equal to 1... Hence IN SUFF

S2: st =1 , r can be 2 ... then rst is not equal to 1.. r can be 1 .. then rst is equal to 1... Hence IN SUFF...

combining I and 2... we can have .. r = 2, s = 1/2, t = 2 Then rst = 2 but we can also have r = 1, s = 1, t =1 Then rst = 1..

Hence E...

Hope this helps! _________________

Cheers! JT........... If u like my post..... payback in Kudos!!

|Do not post questions with OA|Please underline your SC questions while posting|Try posting the explanation along with your answer choice| |For CR refer Powerscore CR Bible|For SC refer Manhattan SC Guide|

Re: GMAT Paper test - Test Code 14 [#permalink]
10 Feb 2010, 12:56

1

This post received KUDOS

Expert's post

loki wrote:

piyatiwari wrote:

Answer: "E" : Both statements not sufficient

Now if both statements are taken together, r=1/3 s=3 and t=1/3 => rst not equal to 1.

hence both the statements are not sufficient.

But from your response above combining the two statements tells us conclusively that rst not eqaul to 1. Therefore combining the two statements is sufficient to answer the question as a 'NO'. So shouldn't the answer be 'C'

Is rst = 1 ?

(1) rs = 1 (2) st = 1

Try r=s=t=1, both statements hold true and rst=1. Try r=s=t=-1, both statements hold true and rst=-1.

Re: GMAT Paper test - Test Code 14 [#permalink]
10 Feb 2010, 12:21

piyatiwari wrote:

Answer: "E" : Both statements not sufficient

Now if both statements are taken together, r=1/3 s=3 and t=1/3 => rst not equal to 1.

hence both the statements are not sufficient.

But from your response above combining the two statements tells us conclusively that rst not eqaul to 1. Therefore combining the two statements is sufficient to answer the question as a 'NO'. So shouldn't the answer be 'C'

Re: GMAT Paper test - Test Code 14 [#permalink]
10 Feb 2010, 12:51

loki wrote:

piyatiwari wrote:

Answer: "E" : Both statements not sufficient

Now if both statements are taken together, r=1/3 s=3 and t=1/3 => rst not equal to 1.

hence both the statements are not sufficient.

But from your response above combining the two statements tells us conclusively that rst not eqaul to 1. Therefore combining the two statements is sufficient to answer the question as a 'NO'. So shouldn't the answer be 'C'

Oh yes. My usual mistake . Thanks so much Loki. This goes directly to my error log.

Re: GMAT Paper test - Test Code 14 [#permalink]
10 Feb 2010, 13:04

Bunuel wrote:

loki wrote:

piyatiwari wrote:

Answer: "E" : Both statements not sufficient

Now if both statements are taken together, r=1/3 s=3 and t=1/3 => rst not equal to 1.

hence both the statements are not sufficient.

But from your response above combining the two statements tells us conclusively that rst not eqaul to 1. Therefore combining the two statements is sufficient to answer the question as a 'NO'. So shouldn't the answer be 'C'

Try r=s=t=1, both statement hold true and rst=1. Try r=s=t=-1, both statement hold true and rst=-1.

OG DS 95, explain how my logic is wrong [#permalink]
14 Feb 2010, 10:19

Ok, without a doubt my number property skills are my achillies heel when is comes to GMAT quant.

I was reviewing my error log today. Tell me why my logic is wrong.

95. Is rst=1

(1) rs=1 (2) st=1

I attacked it by rearranging the original equations, dividing both sides by t.

so, rs=1/t then sub in rs=1 so, 1=1/t then cross multiply t=1 Combined with what we already know (rs=1) we have 1*1=1 Therefore, sufficient.

Same logic can be applied to statment 2. Therefore my answer was D.

OA is actually E and I understand how they got it, but I also fail to see why my strategy was wrong. I feel like I'm probably overlooking some basic rule that governs all equations here but if someone could help me out that'd be great.

Re: OG DS 95, explain how my logic is wrong [#permalink]
14 Feb 2010, 10:36

Currency wrote:

Ok, without a doubt my number property skills are my achillies heel when is comes to GMAT quant.

I was reviewing my error log today. Tell me why my logic is wrong.

95. Is rst=1

(1) rs=1 (2) st=1

I attacked it by rearranging the original equations, dividing both sides by t.

so, rs=1/t then sub in rs=1 so, 1=1/t then cross multiply t=1 Combined with what we already know (rs=1) we have 1*1=1 Therefore, sufficient.

Same logic can be applied to statment 2. Therefore my answer was D.

OA is actually E and I understand how they got it, but I also fail to see why my strategy was wrong. I feel like I'm probably overlooking some basic rule that governs all equations here but if someone could help me out that'd be great.

Thanks

Okay, you can really deal with this much simpler. But, let's review what you've done.

I attacked it by rearranging the original equations, dividing both sides by t. so, rs=1/t

your question then changes to -- Is rs=1/t? 1. Does this give the vale of t? No. Even if you use (1), you get -- 1=1/t -> t=1. Does this answer your question. No. A/D out 2. Similarly, does the value of st=1, help us in answering the question? No. B out

Re: OG DS 95, explain how my logic is wrong [#permalink]
14 Feb 2010, 10:41

Quote:

"The question is asking u to prove that... and you are considering the same as True. This isnt the correct approach."

This is what I was missing. Normally I'd instinctively follow that, but I think cause it was in my error log I over-thought it and got fancy - effectively confusing myself. Ha!

Thanks for the quick repsonses guys, much appreciated! _________________

Its clear that 1 and 2 do not lead to a solution. then, Cant this be solved by observing that we have 2 equations and 3 unknown variables. hence not sufficient and hence E?

Its clear that 1 and 2 do not lead to a solution. then, Cant this be solved by observing that we have 2 equations and 3 unknown variables. hence not sufficient and hence E?

That's not entirely correct. Notice that we are asked to find whether rst = 1, not the values of the unknowns.

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email. _________________