Data Sufficiency (DS) Traps : GMAT Quantitative Section
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# Data Sufficiency (DS) Traps

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05 Apr 2008, 02:44
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Hi friends,

I open this thread because, I think, recognizing a pattern is very helpful in Math, expecially in DS with a very tricky problems. When we are in the battle, time is a gold.

In one long post of Traps Collection of the forum, I found that there was no general discription to differentiate the trap called SPY GIRL. So, if you dont mind, let paste here any problem has E choice as correct one. From that, may we have a rule? what do you think?

I am first.

I. SPY GIRL
1.
What fraction of this year's graduating students at a certain college are males?

a. Of this year's graduating students, 33 percent of the males and 20 percent of the females transferred from another college.
b. Of this year's graduating students, 25 percent transferred from another college.
AC=E

II THE TWIN
1.
Martha bought an armchair and a coffee table at an auctio and sold both items at her store. Her gross profit from the purchase and sale of the armchair was what percent greater than her gross profit from the purchase and sale of the coffee table?

a. Marth paid 10 percent for the armchair than for the coffee table
b. Marth sold the armchair for 20 percent more than she sold the coffee table
AC=E

2. Warehouse W's revenue from the sale of sofas was what percent greater this year than it was last year?

a. Warehouse W sold 10 percent more sofas this year than it did last year

i. Thomas deposited an additional $4,000 throughout the year ii. The checking account earned 7 percent simple interest You cannot assume that the deposits were uniform or in equal installments How many kiloliters of water are in a reservoir? i. If the reservoir were filled to capacity, there would be 430 more kiloliters in the reservoir. ii. The reservoir is normally 65 percent full. We don't know if these are "normal" conditions. Insufficient. 4. What ETS often does on harder DS questions, it gives the first piece of info as insufficient, and then, naturally, you move on to the second and then when you see that it is sufficient, you conclude that both are enough – C. Be careful to evaluate both statements one by one. If it is hard for you, try starting from the second statement instead of the first. 5. When you solve a medium/hard DS question, play a game with ETS, find the answer to the puzzle. If you looked through the both pieces of info and it seems both are sufficient, try proving that one is irrelevant or if both pieces are needed, try to prove that only one will be enough; try challenging the question author; give him a hard time. It will often pay off. 6. Watch out for Yes/No data sufficiency questions. 7. Make an analysis of your mistakes and see what DS questions cause the most problems. 8. Make sure you don’t confuse D and C answer choices _________________ Founder of GMAT Club US News Rankings progression - last 10 years in a snapshot - New! Just starting out with GMAT? Start here... Need GMAT Book Recommendations? Best GMAT Books Co-author of the GMAT Club tests GMAT Club Premium Membership - big benefits and savings Intern Joined: 30 Sep 2009 Posts: 17 Followers: 0 Kudos [?]: 32 [0], given: 0 Re: Data Sufficiency (DS) Traps [#permalink] ### Show Tags 05 Feb 2010, 11:26 I got the spy girl question mentioned at the top no later than this afternoon on a gmat prep test. I answered E but the correct answer given is C. Can someone help please ? What fraction of this year's graduating students at a certain college are males? a. Of this year's graduating students, 33 percent of the males and 20 percent of the females transferred from another college. b. Of this year's graduating students, 25 percent transferred from another college. GMAT Tutor Joined: 24 Jun 2008 Posts: 1183 Followers: 421 Kudos [?]: 1506 [0], given: 4 Re: Data Sufficiency (DS) Traps [#permalink] ### Show Tags 05 Feb 2010, 15:56 arnaudl wrote: I got the spy girl question mentioned at the top no later than this afternoon on a gmat prep test. I answered E but the correct answer given is C. Can someone help please ? What fraction of this year's graduating students at a certain college are males? a. Of this year's graduating students, 33 percent of the males and 20 percent of the females transferred from another college. b. Of this year's graduating students, 25 percent transferred from another college. From S2, if we have m males and f females, (m+f)/4 transfered from another college. From S1, m/3 + f/5 transferred from another college. These are equal: (m + f)/4 = m/3 + f/5 15m + 15f = 20m + 12f 5m = 3f m/f = 3/5 so the ratio of men to women is 3 to 5, and 3/8 of all students are male. Alternatively you could recognize that the two statements combined give us a weighted average situation; from the first statement we know the % from each group who transferred, and from the second statement we know the % of the two groups combined who transferred, from which it is always possible to find the ratio of the two groups; there's no need to calculate anything here. I'm not sure why the answer is indicated as E in the post at the beginning of this thread. _________________ GMAT Tutor in Toronto If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com Manager Status: Preparing myself to break the sound( 700 )-barrier! Affiliations: IFC - Business Edge, Bangladesh Enterprise Institute Joined: 15 Feb 2011 Posts: 209 Location: Dhaka, Bangladesh Schools: Texas A&M - Mays; PennState - Smeal; Purdue - Krannert; JohnsHopkins - Carey; Vanderbilt - Owen; WakeForest - Babcock; UBC - Sauder WE 1: Financial Analyst/Financial Management Trainer - BRAC Afghanistan - 13 months WE 2: Business Proposal Coordinator - MiDS, Inc. (in Kabul, Afghanistan) - 4 Months (did quit the job bcoz of security concerns) WE 3: Readers For Readers (A Social Impact Generating Organization) - Co-Founder Followers: 7 Kudos [?]: 67 [0], given: 136 Re: Data Sufficiency (DS) Traps [#permalink] ### Show Tags 29 Apr 2011, 10:32 Very helpful thread for me. Director Joined: 23 Apr 2010 Posts: 584 Followers: 2 Kudos [?]: 78 [0], given: 7 Re: Data Sufficiency (DS) Traps [#permalink] ### Show Tags 22 Sep 2011, 03:40 Quote: 2. Both statements 1 and 2 are identical but masked. What is the value of x? i. x + 2y = 6 ii. 4y + 2x = 12 So the answer would be E (because x could be anything and the question asks for a precise value of x)? Am I right? Math Forum Moderator Joined: 20 Dec 2010 Posts: 2021 Followers: 161 Kudos [?]: 1705 [0], given: 376 Re: Data Sufficiency (DS) Traps [#permalink] ### Show Tags 22 Sep 2011, 03:45 nonameee wrote: Quote: 2. Both statements 1 and 2 are identical but masked. What is the value of x? i. x + 2y = 6 ii. 4y + 2x = 12 So the answer would be E (because x could be anything and the question asks for a precise value of x)? Yes. Am I right? Yes. _________________ Director Joined: 23 Apr 2010 Posts: 584 Followers: 2 Kudos [?]: 78 [0], given: 7 Re: Data Sufficiency (DS) Traps [#permalink] ### Show Tags 22 Sep 2011, 03:56 Ok. Thanks. Fluke, could you please also take a look at my question in this thread: last-digit-of-a-power-70624-60.html ? The last post. Thanks. Intern Joined: 11 Sep 2012 Posts: 1 Followers: 0 Kudos [?]: 0 [0], given: 1 Re: Data Sufficiency (DS) Traps [#permalink] ### Show Tags 25 Oct 2012, 21:07 fluke wrote: nonameee wrote: Quote: 2. Both statements 1 and 2 are identical but masked. What is the value of x? i. x + 2y = 6 ii. 4y + 2x = 12 So the answer would be E (because x could be anything and the question asks for a precise value of x)? Yes. Am I right? Yes. if v combine the 2 stmnts v can gt the value of x . so shudnt the answer be C ?? plz correct me if im wrong Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7125 Location: Pune, India Followers: 2137 Kudos [?]: 13681 [0], given: 222 Re: Data Sufficiency (DS) Traps [#permalink] ### Show Tags 26 Oct 2012, 04:41 Shivani16 wrote: nonameee wrote: What is the value of x? i. x + 2y = 6 ii. 4y + 2x = 12 So the answer would be E (because x could be anything and the question asks for a precise value of x)? Yes. Am I right? if v combine the 2 stmnts v can gt the value of x . so shudnt the answer be C ?? plz correct me if im wrong That's the trap here! Stmnt 1: x + 2y = 6 Stmnt 2: 4y + 2x = 12 which is same as 2y + x = 6 (divide LHS and RHS by 2) Notice that stmnts 1 and 2 are essentially the same. We don't really have two equations to solve for x and y. They are the same equation. One equation is not sufficient and hence the answer will be E. _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

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11 Dec 2015, 14:28
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08 Jan 2017, 09:12
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Re: Data Sufficiency (DS) Traps   [#permalink] 08 Jan 2017, 09:12
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