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Problem Solving — algebra and arithmetic (GMAT Focus Edition)
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Quant #5

by anirudhbhalotia » Thu Nov 25, 2010 7:11 am
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This one totally fried my brains!

I wasted almost 5 mins on this one, but was so confused and had to make a random guess to move on. Guess was wrong!


Kindly explain!

Is there a particular concept behind these questions so that we can understand and not fall in the "trap" ?
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by Geva@EconomistGMAT » Thu Nov 25, 2010 12:23 pm
What you need is a way to organize the information so your brain keeps cool. What we have here is a sets table question, solvable by a 3*3 grid: put like/dislike lima in the columns, like/dislike Brussels sprouts in the rows, and don't forget a total column and row. Then organize the information in the question stem and statements, clearly mark which box you need to find, and see if the information you have allows you to reach that box.

The attached file shows the tables for stat. (1) and (2).
Stat. (1) is sufficient because you can reach the like BS / dislike Lima box:
120 total / total students.
2/3 of those dislike Lima = 80 (goes in Dislike Lima / Total)
3/5 of the 80 also dislike BS = 48 (goes in dislike Lima / dislike BS)
The remaining 32 are the required dislike Lima / like BS, so stat. (1) is sufficient.

Stat. (2) is also sufficient: if 40 of the students like Lima, and we know that 2/3 of the students dislike Lima, then the 40 lima likers constitute the remaining 1/3 of the students. if 40 is 1/3 of the total/total (marked as X), then the total students is 3*40 = 120 - and the rest is the same as stat. (1). The two statements basically say the same thing.
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by rishab1988 » Thu Nov 25, 2010 3:48 pm
Here is how I approached the problem.(solved in under 2 minutes)

I assumed let no of students be =30 [divisible by both 3 and 5]


Like Dislike

Sprouts - -
Lima - 20 (2/3*10)



Like Dislike

Sprouts - 12 (3/5*20)
Lima - 20


Like Dislike

Sprouts - 12
Lima 10 20 [ total no of students =30 and there is no intersection of Like and dislike Lima beans]


Like Dislike

Sprouts 18 12 [same reason -total students =30]
Lima 10 20


Now question was Like sprout + dislike lima = 18 [like spout]-10[like Lima]=8 Dislike Lima

SO we can infer,if we know the number of students,we can find the answer

1) sufficient
2) Lets x= no of students
2/3x=dislike lima beans
then 1/3 like lima beans

1/3x=40 or x=120 [same as 1].sufficient

My answer D

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by anirudhbhalotia » Thu Nov 25, 2010 10:24 pm
Geva@MasterGMAT wrote:What you need is a way to organize the information so your brain keeps cool. What we have here is a sets table question, solvable by a 3*3 grid: put like/dislike lima in the columns, like/dislike Brussels sprouts in the rows, and don't forget a total column and row. Then organize the information in the question stem and statements, clearly mark which box you need to find, and see if the information you have allows you to reach that box.

The attached file shows the tables for stat. (1) and (2).
Stat. (1) is sufficient because you can reach the like BS / dislike Lima box:
120 total / total students.
2/3 of those dislike Lima = 80 (goes in Dislike Lima / Total)
3/5 of the 80 also dislike BS = 48 (goes in dislike Lima / dislike BS)
The remaining 32 are the required dislike Lima / like BS, so stat. (1) is sufficient.

Stat. (2) is also sufficient: if 40 of the students like Lima, and we know that 2/3 of the students dislike Lima, then the 40 lima likers constitute the remaining 1/3 of the students. if 40 is 1/3 of the total/total (marked as X), then the total students is 3*40 = 120 - and the rest is the same as stat. (1). The two statements basically say the same thing.


Geva - Nice! Was totally able to get the concept. Can we say that all like/dislikes types of question can be solved using the set table way?


Rishab1988 - Your way even though it works, seems a bit complicated to me compared to Geva's solution!


Thanks to both of you for chipping in!