It is currently 20 Apr 2018, 05:54

Close

GMAT Club Daily Prep

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.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

Of the N students in a certain class, X took a course in biology and Y

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Intern
Intern
avatar
Joined: 26 Sep 2012
Posts: 34
Of the N students in a certain class, X took a course in biology and Y [#permalink]

Show Tags

New post 03 Jul 2014, 23:57
2
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  85% (hard)

Question Stats:

61% (01:37) correct 39% (02:01) wrong based on 117 sessions

HideShow timer Statistics

Of the N students in a certain class, X took a course in biology and Y took a course in history, and Z took neither of the courses. If there were students who took both two courses, in terms of N, X, Y and Z, what fraction of the students took both two courses?


(A) \(1 - \frac{X+Y+Z}{N}\)

(B) \(\frac{X+Y+Z}{N} - 1\)

(C) \(\frac{X+Y-Z-N}{N}\)

(D) \(\frac{N+X+Y-Z}{N}\)

(E) \(\frac{N-X-Y+Z}{N}\)
[Reveal] Spoiler: OA
Senior Manager
Senior Manager
User avatar
Joined: 13 Jun 2013
Posts: 277
Premium Member
Re: Of the N students in a certain class, X took a course in biology and Y [#permalink]

Show Tags

New post 04 Jul 2014, 02:50
Maksym wrote:
Of the N students in a certain class, X took a course in biology and Y took a course in history, and Z took neither of the courses. If there were students who took both two courses, in terms of N, X, Y and Z, what fraction of the students took both two courses?

(A) 1 - (X+Y+Z) / N
(B) (X+Y+Z) / N - 1
(C) (X+Y-Z-N) / N
(D) (N+X+Y-Z) / N
(E) (N-X-Y+Z) / N


N= x+y-both + z

both= x+y+z-N

thus fraction becomes, (x+y+z-N)/N
= ((x+y+z)/N)-1
B
Intern
Intern
avatar
Joined: 02 Feb 2016
Posts: 15
Re: Of the N students in a certain class, X took a course in biology and Y [#permalink]

Show Tags

New post 07 Mar 2016, 13:42
manpreetsingh86 wrote:
Maksym wrote:
Of the N students in a certain class, X took a course in biology and Y took a course in history, and Z took neither of the courses. If there were students who took both two courses, in terms of N, X, Y and Z, what fraction of the students took both two courses?

(A) 1 - (X+Y+Z) / N
(B) (X+Y+Z) / N - 1
(C) (X+Y-Z-N) / N
(D) (N+X+Y-Z) / N
(E) (N-X-Y+Z) / N


N= x+y-both + z

both= x+y+z-N

thus fraction becomes, (x+y+z-N)/N
= ((x+y+z)/N)-1
B


Hi!

It's absolutely clear how you got both= x+y+z-N, but what did you do to get the next equation? And where does N-1 in denominator come from?

Thanks a lot!
Expert Post
1 KUDOS received
Math Expert
User avatar
V
Joined: 02 Aug 2009
Posts: 5769
Re: Of the N students in a certain class, X took a course in biology and Y [#permalink]

Show Tags

New post 07 Mar 2016, 19:45
1
This post received
KUDOS
Expert's post
1
This post was
BOOKMARKED
Viktoriaa wrote:
manpreetsingh86 wrote:
Maksym wrote:
Of the N students in a certain class, X took a course in biology and Y took a course in history, and Z took neither of the courses. If there were students who took both two courses, in terms of N, X, Y and Z, what fraction of the students took both two courses?

(A) 1 - (X+Y+Z) / N
(B) (X+Y+Z) / N - 1
(C) (X+Y-Z-N) / N
(D) (N+X+Y-Z) / N
(E) (N-X-Y+Z) / N


N= x+y-both + z

both= x+y+z-N

thus fraction becomes, (x+y+z-N)/N
= ((x+y+z)/N)-1
B


Hi!

It's absolutely clear how you got both= x+y+z-N, but what did you do to get the next equation? And where does N-1 in denominator come from?

Thanks a lot!


Hi,

let me take it from where you left..
both= x+y+z-N..
But we have to find the fraction..
\(Fraction = \frac{Both}{total}= \frac{both}{N}\)
=> \(\frac{(x+y+z-N)}{N}= \frac{(x+y+z)}{N}-\frac{N}{N}\)
=> \(\frac{(x+y+z)}{N}-1\)

Hope it helps you

_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html


GMAT online Tutor

Intern
Intern
avatar
Joined: 02 Feb 2016
Posts: 15
Re: Of the N students in a certain class, X took a course in biology and Y [#permalink]

Show Tags

New post 08 Mar 2016, 05:39
Got it, thank you! I should read questions more carefully.
Manager
Manager
avatar
B
Joined: 05 Dec 2015
Posts: 123
Premium Member Reviews Badge
Re: Of the N students in a certain class, X took a course in biology and Y [#permalink]

Show Tags

New post 29 Jun 2016, 23:59
Hello - I'm having trouble understanding why using smart numbers isn't working, can someone assess my method please?

N students: 10
X Bio: 3
Y History: 5
Z Neither: 5

Formula: N = X + Y + Z - Both --> 10 = 3 + 5 + 5 - both --> both = 3

Plug variables into answer B gives you: (X+Y+Z) / N - 1 --> (3 + 5 + 5)/10-1 --> gives you 13/10 - 1 or 13/9 depending on whether the denominator is (N-1) or only /N, but either way does not equal 30% (3/10) as I would expect
Non-Human User
User avatar
Joined: 09 Sep 2013
Posts: 6645
Premium Member
Re: Of the N students in a certain class, X took a course in biology and Y [#permalink]

Show Tags

New post 13 Mar 2018, 11:02
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

Re: Of the N students in a certain class, X took a course in biology and Y   [#permalink] 13 Mar 2018, 11:02
Display posts from previous: Sort by

Of the N students in a certain class, X took a course in biology and Y

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.