overlapping set

Expert replies

ildude02: Master | Next Rank: 500 Posts; Posts: 320; Joined: Sun Jan 13, 2008 10:00 pm; Thanked: 10 times

by ildude02 » Sat Sep 20, 2008 8:35 pm

I have a general question with regards to the usage of "or" and "and" in a set theory question. Eg;

A class consists of math or science students. If the total number of the students is 200, how many are science students?

--in trying to find the unknown variables before we determine the sufficiency, do we need to consider the "intersection" of Math and science students for this question? Or, can we consider the intersection to NULL since we say "Math OR science " adn just have the below eq,

Total = Math + Science(basically not considering "Intersection" and"neither"). Appreciate anyones responce.

Source: Beat The GMAT — Data Sufficiency | Sat Sep 20, 2008 8:35 pm

niraj_a: Legendary Member; Posts: 708; Joined: Sun Jun 01, 2008 4:59 amFollowed by: 1 member; Location: USA; Thanked: 13 times

by niraj_a » Sun Sep 21, 2008 7:55 am

id suggest that for questions like these you create a 2 column x 2 row matrix like so:

Science Not Science
Math

Not Math
-------------------------------------------------------------
Total Number

Then you can add the given details in the appropriate boxes and find what is needed that way.

Hope this helped.

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Ian Stewart: GMAT Instructor; Posts: 2623; Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members; Location: Montreal; Thanked: 1090 times; GMAT Score:780

Re: overlapping set

by Ian Stewart » Sun Sep 21, 2008 9:02 am

ildude02 wrote:I have a general question with regards to the usage of "or" and "and" in a set theory question. Eg;

A class consists of math or science students. If the total number of the students is 200, how many are science students?

It's really a hypothetical question- on a real GMAT question, the wording will make it absolutely clear whether there can be students who are both math and science students, or whether that is impossible. If there's a particular question you've seen in GMATPrep or some other official GMAT publication which you found ambiguous, post the exact wording here, but I can assure you it will be clear to you on the test whether the groups can overlap.

For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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