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Day 4. Data Sufficiency - Video 10 - Useful Contradictions

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baixa2329: Newbie | Next Rank: 10 Posts; Posts: 6; Joined: Thu Mar 15, 2012 12:54 pm

Day 4. Data Sufficiency - Video 10 - Useful Contradictions

by baixa2329 » Sat Mar 31, 2012 7:06 am

The question that I have, is about the 10th video of the day 4.
In the last example, if I follow what I've learned, just by looking at statement 1 I'ld say that is sufficient, because I can find x. Furthermore, statement 2 would be sufficient.
I know that I don't have to make calculations, in order to save time, but in this kind of question if I don't make them I'ld be wrong, answering D, instead of C.
So what is the right method???

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Source: Beat The GMAT — The 60-Day GMAT Study Guide | Sat Mar 31, 2012 7:06 am

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by Brent@GMATPrepNow » Sat Mar 31, 2012 7:27 am

baixa2329 wrote:The question that I have, is about the 10th video of the day 4.
In the last example, if I follow what I've learned, just by looking at statement 1 I'ld say that is sufficient, because I can find x. Furthermore, statement 2 would be sufficient.
I know that I don't have to make calculations, in order to save time, but in this kind of question if I don't make them I'ld be wrong, answering D, instead of C.
So what is the right method???

Sometimes you do have to perform calculations to answer a DS question, and sometime you don't have to perform calculations.

If the target question asked us to find the value of x, and a statement told us that 1.324x + 42.23 = 10.2, then I would know that I have sufficient information, without performing calculations. I know that this linear equation will yield only one solution, so I won't waste time performing calculations.

However, if the target question asked us to find the value of x, and a statement told us that x^2 + 5x + 6 = 0, then I need to recognize that quadratic equations may have 2 different solutions, in which case I may need to perform some calculations to determine whether the statement provides sufficient information.

I hope that helps.

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com