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Does abcd = 1? (1) abc = 1 (2) bcd = 1

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Does abcd = 1? (1) abc = 1 (2) bcd = 1 [#permalink] New post 03 Mar 2011, 11:27
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A
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E

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100% (01:24) correct 0% (00:00) wrong based on 3 sessions
Q. Does abcd = 1?

(1) abc = 1
(2) bcd = 1

Without any work, explain why must the answer be TOGETHER NOT sufficient?

Solution:

[Reveal] Spoiler:
The question asks whether the product of four variables will be 1. The variables are completely unqualified, so to answer this question something must be known about each variable.

Statement (1) provides a relationship between three of the variables so it is insufficient.

Statement (2) provides a relationship between three of the variables so it is insufficient.

This eliminates three answers choices.

Taken together the Statements do provide information about all four variables, but is that information enough? Let's use the Schrute test.

Dwight Schrute once said, "Whenever I'm about to do something, I think, "Would an idiot do that?" And if they would, I do not do that thing."

Let's modify this for the GMAT: "Whenever I'm about to pick an answer, I think, "Would a typical GMAT taker pick that answer?"And if they would, I do not pick that answer."

Would a typical GMAT taker think that Statements (1) and (2) were sufficient? Yes, he would. Therefore we must pick TOGETHER NOT sufficient.
[Reveal] Spoiler: OA

Last edited by spacelandprep on 03 Mar 2011, 20:31, edited 2 times in total.
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Re: Spaceland Prep Strategy Question #1 [#permalink] New post 03 Mar 2011, 11:33
We want to find out is abcd = 1

Statement 1 says abc = 1. It doesn't say anything about d, so insufficient

Statement 2 says bcd = 1. It doesn't say anything about a, so insufficient

Combining 1 and 2, we get a(bc)(bc)d=1

or abcd*bc = 1

Now abcd would be 1 only if bc = 1, but neither 1 nor 2 nor them combined can definitely tell us that bc = 1. Fore.g., bc can be 1/2 and a=2 and d = 2 and both statements can be satisfied.
So, answer should be E
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Re: Spaceland Prep Strategy Question #1 [#permalink] New post 03 Mar 2011, 19:05
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spacelandprep wrote:
The question asks whether the product of four variables will be 1. The variables are completely unqualified, so to answer this question something must be known about each variable.


I've seen prep company representatives repeat this idea in many places, and it's mathematical nonsense. If you change your question to:

Does abcd = 0?
(1) abc = 0
(2) bcd = 0


then you certainly do not need to know 'about each variable' to answer the question; the answer is D even though we don't know the value of any of the variables. There are many official DS questions with multiple unknowns which follow a similar pattern - the question asks for the value of some combination of unknowns, and while you cannot determine the value of the unknowns themselves, you can still answer the question. Q168 in the DS section of OG12 is one of many examples.

spacelandprep wrote:
Let's modify this for the GMAT: "Whenever I'm about to pick an answer, I think, "Would a typical GMAT taker pick that answer?"And if they would, I do not pick that answer."


There are many GMAT questions which are genuinely simple. Applying this test to real GMAT questions could easily lead a test taker to 'outsmart' him or herself, and pick the wrong answer rather than the correct one. While I agree one should be suspicious of 'obvious' answers in DS, the safest thing for the test taker to do is to understand the math involved, rather than apply gimmicky 'tricks' which will only give you the right answer some of the time.
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Re: Spaceland Prep Strategy Question #1 [#permalink] New post 03 Mar 2011, 20:25
Well said Ian +1.

I would be wary of any strategy which would want me to take a decision based on my limited understanding of what a "typical" GMAT taker would do.

Much easier and simpler to stick to the underlying Math - it would work every time.
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Re: Spaceland Prep Strategy Question #1 [#permalink] New post 03 Mar 2011, 20:54
IanStewart wrote:
spacelandprep wrote:
The question asks whether the product of four variables will be 1. The variables are completely unqualified, so to answer this question something must be known about each variable.


I've seen prep company representatives repeat this idea in many places, and it's mathematical nonsense. If you change your question to:

Does abcd = 0?
(1) abc = 0
(2) bcd = 0


then you certainly do not need to know 'about each variable' to answer the question; the answer is D even though we don't know the value of any of the variables. There are many official DS questions with multiple unknowns which follow a similar pattern - the question asks for the value of some combination of unknowns, and while you cannot determine the value of the unknowns themselves, you can still answer the question. Q168 in the DS section of OG12 is one of many examples.


It is true that something must be known about each variable for Q168. The sufficient statement mentions both variables.

IanStewart wrote:
spacelandprep wrote:
Let's modify this for the GMAT: "Whenever I'm about to pick an answer, I think, "Would a typical GMAT taker pick that answer?"And if they would, I do not pick that answer."


There are many GMAT questions which are genuinely simple. Applying this test to real GMAT questions could easily lead a test taker to 'outsmart' him or herself, and pick the wrong answer rather than the correct one. While I agree one should be suspicious of 'obvious' answers in DS, the safest thing for the test taker to do is to understand the math involved, rather than apply gimmicky 'tricks' which will only give you the right answer some of the time.


While knowing the math is the safest route to a correct answer, it's not always a possible route. Familiarity with the mathematical concepts covered on the GMAT is essential but sometimes a question is simply going to be beyond you, well maybe not you, but some of us. Having an alternate form of approach is necessary in those instances. It's by no means a guarantee, but anything that improves the odds of getting a tough question correct when using math is not an option is a great tool.
Re: Spaceland Prep Strategy Question #1   [#permalink] 03 Mar 2011, 20:54
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