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In a class of 200 students, forty percent are girls.

This topic has 2 expert replies and 0 member replies

In a class of 200 students, forty percent are girls.

Post Fri Nov 10, 2017 6:18 am
In a class of 200 students, forty percent are girls. Twenty-five percent of the boys and 10 percent of the girls signed up for a tour to Washington DC. What percent of the class signed up for the tour?

(A) 19%
(B) 23%
(C) 25%
(D) 27%
(E) 35%

The OA is A .

I got confused making the calculus. Experts, may you explain it to me step by step? Thanks.

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GMAT/MBA Expert

Post Fri Nov 10, 2017 7:29 am
I thought I'd point out that Ceilidh's "Overlapping Sets matrix" approach is also known as the Double Matrix Method. This technique can be used for most questions featuring a population in which each member has two characteristics associated with it.

Here, we have a population of students, and the two characteristics are:
- boy or girl
- signed up for tour or didn't sign up for tour

This question type is VERY COMMON on the GMAT, so be sure to master the technique.

To learn more about the Double Matrix Method, watch this video: http://www.gmatprepnow.com/module/gmat-word-problems?id=919

Once you’re familiar with this technique, you can attempt these additional practice questions:

Easy Problem Solving questions
- http://www.beatthegmat.com/finance-majors-non-finance-majors-overlapping-set-question-t167425.html

Medium Problem Solving questions
- http://www.gmatprepnow.com/module/gmat-word-problems/video/920
- http://www.beatthegmat.com/posted-speed-limit-t272374.html
- http://www.beatthegmat.com/motel-t271938.html
- http://www.beatthegmat.com/of-the-applicants-passes-a-certain-test-15-t270255.html
- http://www.beatthegmat.com/opening-night-and-late-patrons-t264869.html
- http://www.beatthegmat.com/at-least-100-students-at-a-certain-high-school-study-japanes-t274669.html
- http://www.beatthegmat.com/prblem-solving-t279424.html

Difficult Problem Solving questions
- http://www.gmatprepnow.com/module/gmat-word-problems/video/946
- http://www.beatthegmat.com/ratio-problem-t268339.html
- http://www.beatthegmat.com/overlapping-sets-question-t265223.html
- http://www.beatthegmat.com/fractions-t264254.html
- http://www.beatthegmat.com/overlapping-sets-t264092.html
- http://www.beatthegmat.com/mba/2011/05/09/random-double-matrix-question-2

Easy Data Sufficiency questions
- http://www.gmatprepnow.com/module/gmat-word-problems/video/943
- http://www.beatthegmat.com/for-what-percent-of-those-tested-for-a-certain-t270596.html
- http://www.beatthegmat.com/ds-quest-t187706.html

Medium Data Sufficiency questions
- http://www.beatthegmat.com/sets-matrix-ds-t271914.html
- http://www.beatthegmat.com/each-of-people-voted-once-in-an-election-x-t271375.html
- http://www.beatthegmat.com/a-manufacturer-t270331.html
- http://www.beatthegmat.com/in-costume-for-halloween-t269355.html
- http://www.beatthegmat.com/mba/2011/05/05/random-double-matrix-question-1

Difficult Data Sufficiency questions
- https://youtu.be/dsCeqF9Kbk8
- http://www.beatthegmat.com/double-set-matrix-question-t271423.html
- https://youtu.be/dOZ9KM1m5Hs
- http://www.beatthegmat.com/sets-t269449.html
- http://www.beatthegmat.com/mba/2011/05/16/random-double-matrix-question-3

Cheers,
Brent

_________________
Brent Hanneson – Founder of GMATPrepNow.com
Use our video course along with Beat The GMAT's free 60-Day Study Guide

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GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months!
Post Fri Nov 10, 2017 7:15 am
Someday soon, the GMAT is going to stop writing problems that assume that gender is binary. The GRE correctly made this change in the newest edition of its OG; we can assume the GMAT will follow suit.

But... assuming that this particular question assumes that "boys" and "girls" are the only categories that exist, we can set this up using Overlapping Sets matrix:



Now, fill in what you know:


Add the information about percentages of each group going on the tour:


38 students are signed up for the tour. Be careful, though! The question does not ask us for the number, it asks for the percentage:
38 is what percent of 200? --> 19%

The answer is A.

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Ceilidh Erickson
Manhattan Prep GMAT & GRE instructor
EdM in Mind, Brain, and Education
Harvard Graduate School of Education


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