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• ### $450 Tuition Credit & Official CAT Packs FREE December 15, 2018 December 15, 2018 10:00 PM PST 11:00 PM PST Get the complete Official GMAT Exam Pack collection worth$100 with the 3 Month Pack ($299) • ### FREE Quant Workshop by e-GMAT! December 16, 2018 December 16, 2018 07:00 AM PST 09:00 AM PST Get personalized insights on how to achieve your Target Quant Score. # A jar contains red and green marbles, available in two sizes- small  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics Author Message TAGS: ### Hide Tags Current Student Joined: 22 Jul 2014 Posts: 123 Concentration: General Management, Finance GMAT 1: 670 Q48 V34 WE: Engineering (Energy and Utilities) A jar contains red and green marbles, available in two sizes- small [#permalink] ### Show Tags 04 Sep 2014, 23:43 3 00:00 Difficulty: 45% (medium) Question Stats: 65% (01:48) correct 35% (02:48) wrong based on 101 sessions ### HideShow timer Statistics A jar contains red and green marbles, available in two sizes- small and big. 20% of the marbles are red and 60% of the marbles are small. How many small green marbles does the jar contain? (1) The total number of green marbles is 80. (2) 10% of total marbles in the jar are small and red Source: 4Gmat I remember the instructor suggesting that such problems with 3 variables can be solved using the table method. Can someone help me with it. Also I would like to know the conventional method. I freeze when I see such problems Manager Joined: 29 Apr 2014 Posts: 67 Location: India Concentration: Other, Finance GMAT 1: 770 Q51 V42 WE: Analyst (Retail Banking) Re: A jar contains red and green marbles, available in two sizes- small [#permalink] ### Show Tags 05 Sep 2014, 00:18 1 1 alphonsa wrote: A jar contains red and green marbles, available in two sizes- small and big. 20% of the marbles are red and 60% of the marbles are small. How many small green marbles does the jar contain? 1) The total number of green marbles is 80. 2) 10% of total marbles in the jar are small and red Let's assume the total number of marbles be $$100x$$. (We can't use just the number 100 here because statement (1) mentions the number of green marbles explicitly) Let's draw a table as below and fill it with the information we have from the question stem. In the table, all the rows and columns sum up to the total row or column and the two totals will sum up to the big total in the bottom right corner. P.S. - I don't exactly know how to draw a table here so bear with me. I have used * to indicate blank columns to preserve the table structure (Consecutive spaces get compressed into one ) * | R | G | Total --|-----|-----|------ S | *** | *** | 60x --|-----|-----|------ B | *** | *** | 40x --|-----|-----|------ T |20x|80x|100x 1) The total number of green marbles is $$80$$ So, we know x = 1 and the table becomes * | R | G | Total --|-----|-----|------ S | *** | *** | 60 --|-----|-----|------ B | *** | *** | 40 --|-----|-----|------ T | 20 | 80 | 100 But we can't find the answer. ----> Insufficient 2) 10% of total marbles in the jar are small and red So, small & red = $$10x$$ and the table becomes * | R | G | Total --|-----|-----|------ S |10x|50x| 60x --|-----|-----|------ B |10x|30x| 40x --|-----|-----|------ T |20x|80x|100x We know that small & green = $$50x$$ but have no idea about the value of x. ----> Insufficient 1) and 2) We know $$SG = 50x$$ and $$x = 1$$ ----> Sufficient So, the answer is C. Hope that helps _________________ Psst...If that helped press the thumb on the left Intern Joined: 16 May 2013 Posts: 20 Re: A jar contains red and green marbles, available in two sizes- small [#permalink] ### Show Tags 05 Sep 2014, 10:04 2 Hi, Nicely explained by eshan429 Given : 20% red and 60% small Let total be 100x Red = 20x implies Green = 80x Small =60x implies not small = 40x from (1) we have 80x=80 -> x=1 Still,for knowing the distribution of red small ball or green small ball we must know the color distribution among small balls.So insufficient. from (2) we get 10x = red and small implying 50x = green and small but here we do not know the value of x.So insufficient. Combining 1 and 2 we get the answer..C This method just saves the time of drawing tables,but IMO it generally leads to confusion so it is better to approach these type of questions using tabular method. _________________ Press Kudos!! if you like my post !!! Current Student Joined: 22 Jul 2014 Posts: 123 Concentration: General Management, Finance GMAT 1: 670 Q48 V34 WE: Engineering (Energy and Utilities) Re: A jar contains red and green marbles, available in two sizes- small [#permalink] ### Show Tags 05 Sep 2014, 23:46 Thanks a ton.. Seems easy now Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6639 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: A jar contains red and green marbles, available in two sizes- small [#permalink] ### Show Tags 20 Sep 2015, 00:02 Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution. A jar contains red and green marbles, available in two sizes- small and big. 20% of the marbles are red and 60% of the marbles are small. How many small green marbles does the jar contain? (1) The total number of green marbles is 80. (2) 10% of total marbles in the jar are small and red Transforming the original condition and the question, we have the below 2by2 table that is common in GMAT math test. Attachment: GC DS alphonsa A jar contains red and green marbles(20150918).png [ 2.78 KiB | Viewed 891 times ] there are 4 variables (a,b,c,d) and 2 equations (a+c=20%(a+b+c+d), a+b=60%(a+b+c+d)) therefore we need 2 more equations to match the number of variables and equations. Since there is 1 each in 1) and 2), C has high probability of being the answer and it turns out that C actually is the answer. Normally for cases where we need 2 more equations, such as original conditions with 2 variable, or 3 variables and 1 equation, or 4 variables and 2 equations, we have 1 equation each in both 1) and 2). Therefore C has a high chance of being the answer, which is why we attempt to solve the question using 1) and 2) together. Here, there is 70% chance that C is the answer, while E has 25% chance. These two are the key questions. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since C is most likely to be the answer according to DS definition, we solve the question assuming C would be our answer hence using ) and 2) together. (It saves us time). Obviously there may be cases where the answer is A, B, D or E. _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$99 for 3 month Online Course"
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Re: A jar contains red and green marbles, available in two sizes- small  [#permalink]

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31 Dec 2017, 11:18
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Re: A jar contains red and green marbles, available in two sizes- small &nbs [#permalink] 31 Dec 2017, 11:18
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