Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

A better GRE prep experience. We believe GRE prep should be real education that prepares you not just for the test, but for the challenges you’ll face as you earn your graduate degree and advance your career.

QOTD # 11 Of the students in a school, 20 percent are in the [#permalink]
13 Sep 2016, 06:11

Expert's post

00:00

Question Stats:

58% (01:43) correct
41% (02:03) wrong based on 70 sessions

Of the students in a school, 20 percent are in the science club and 30 percent are in the band. If 25 percent of the students in the school are in the band but are not in the science club, what percent of the students who are in the science club are not in the band?

Re: QOTD # 11 Of the students in a school, 20 percent are in the [#permalink]
20 Sep 2016, 12:13

2

This post received KUDOS

Expert's post

Explanation

Use 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 (aka overlapping sets questions). Here, we have a population of students, and the two characteristics are: - in the science club or not in the science club - in the band or not in the band

So, we can set up our matrix as follows:

Since we aren't told the total population AND we're asked to find a percentage, let's say that the TOTAL population is 100 (an easy number to work with)

20 percent of the students are in the science club, and 30 percent of the students are in the band Since the total population is 100, this means that there are 20 students in the science club. Also, since there are 100 students, we can conclude that 80 students are NOT in teh science club. Likewise, if 30 students are in the band, then 70 students are NOT in the band. So, let's add all of this to the diagram:

25 percent of the students in the school are in the band but are not in the science club Great. We'll add this to our diagram:

Since the two boxes in the left-hand column must add to 30, we can see that the top box must hold 5 students

Since the two boxes in the top row must add to 20, we can see that the top right box must hold 15 students

Using similar logic, we can see that the last box holds 55 students

What percent of the students who are in the science club are not in the band? Our diagram tells us that there are 20 students in the science club. Of those 20 students, 15 are NOT in the band. 15/20 = 75%

Answer: E

RELATED VIDEO

_________________

Brent Hanneson – Creator of greenlighttestprep.com Sign up for my free GRE Question of the Dayemails

Re: QOTD # 11 Of the students in a school, 20 percent are in the [#permalink]
09 May 2020, 11:24

Hi Brent,

Would the answer have been 15% if the question asked "what percent of students are in the science club but are not in the band?" So in this case it would be students who are in science but not in band over the total number of students. I think the reason I got confused with the original question was because I was finding the percentage of students who were in science and not in band from the overall total number of students instead of calculating the percent as a total of students who took Science.

Re: QOTD # 11 Of the students in a school, 20 percent are in the [#permalink]
09 May 2020, 13:20

1

This post received KUDOS

Expert's post

GREStudent2020 wrote:

Hi Brent,

Would the answer have been 15% if the question asked "what percent of students are in the science club but are not in the band?" So in this case it would be students who are in science but not in band over the total number of students. I think the reason I got confused with the original question was because I was finding the percentage of students who were in science and not in band from the overall total number of students instead of calculating the percent as a total of students who took Science.

That's correct. 15 percent of all students are in the science club but not in the band.

Cheers, Brent
_________________

Brent Hanneson – Creator of greenlighttestprep.com Sign up for my free GRE Question of the Dayemails