Overlapping sets Fast.

Question

Hi all

I found that i am taking around 3- 3.5 mins for overlapping sets.Ofcourse ,i could sense it while I was doing,but heard from the Manhattan Assesment.Is there are any trick to cut it to a lesser.My biggest problem is I am randomly guessing last 6 questions.

Thanks
GN :oops:

FuzzyBuzzard · Answer

you should use the double matrix system, as it makes these questions much simpler.
Usually you're dealing with 2 groups of types of items, so you name them A and B. You build a matrix of 3*3 and name the columns "A", "Not A" and "Total", and name the rows "B", "Not B" and "Total". 
The bottom right cell is the total of the cells above it, and also of the cells left of it.

______||___A___|___Not-A__|__Total___
__B___||_______|__________|_________
Not_B_||_______|__________|_________
Total_||_______|__________|__TOTAL__

Now you should carefully read the question stem, and position the values given in the appropriate cells.

See  at-a-certain-hospital  question for usage examples. You can search for overlapping sets question to find moreexamples of this method. it makes OS questions much much easier and quicker to solve!

BN1989 · Answer

I do overlapping sets with 2 categories the same way. You just have to pay attention to the wording of the question, more difficult questions give a percentage value or fraction value of another "cell", whose value is not given, but just a variable. If you do that, you can really save a lot of time on these questions.

KarishmaB · Answer

Most of the sets questions can be easily solved by visualizing using venn diagrams. Chances of making a mistake also reduce. If you have a particular question in mind, put it up and we can provide a less than 2 min solution.

Carcass · Answer

Hi Karishma

Surfing gmatclub I found this post a-polling-company-found-that-of-300-households-surveyed-102377.html#p1098282 where I encountered a formula that I never seen before, neither on MGMAT guide or kaplan (the only formula) and in this one formulae-for-3-overlapping-sets-69014.html#p729340 is an amazing explanation by Bunuel on different kind formulas on OS.

Do you think I have to worry about of all this stuff or all OS are the same problems with slight variations and (as usual) to use logic ??

Thanks

cyberjadugar · Answer

Hi,

Here are some solutions posted by me, check them out. Hope you find them useful.
 https://gmatclub.com/forum/a-polling-company-found-that-of-300-households-surveyed-102377.html#p1098254 
 https://gmatclub.com/forum/a-student-has-decided-to-take-gmat-and-toefl-examinations-134683.html#p1098262 
 https://gmatclub.com/forum/among-a-group-of-2-500-people-35-percent-invest-in-134499.html#p1096610 
 https://gmatclub.com/forum/in-a-survey-of-retailers-what-percent-had-purchased-134506.html#p1096604 
 https://gmatclub.com/forum/of-the-300-subjects-who-participated-in-an-experiment-using-134147.html#p1094343

Regards,

KarishmaB · Answer

I am not a fan of using formulas until and unless they are intuitive (logical) or useful in many cases. As for these two formulas, they are exactly same (obviously) and you don't need to learn them at all. All you need to do it draw the diagram and know exactly which region represents what and what is given to you. e.g. you must know which region is "only A", which region is "A", which region represents "A and B", which represents "Only A and B" etc. Depending on what is given, you can easily find what you need to find by just looking at the diagram. You can derive both the formulas on your own by just looking at the diagram. 
As Bunuel noted too:
"I'd advise to understand the concept rather than to memorize formulas."

Go through the thread and ensure you understand everything. Thereafter, you can just draw the diagram and solve any problem.

gmatsaga · Answer

Besides writing the double-matrix quickly, I think your overall duration for an overlapping set problem is hinged on your comprehension of the problem. Most people spend too much time in an overlapping set question because they don't know which box to fill up.

And yes, this could only be improved by answering a multitude of overlapping sets questions.

Carcass · Answer

Thanks I'll do it. either case is a minor area of concentration .........

Overlapping sets Fast.

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