At the beginning of a class, a classroom has 3 empty chairs and all students are seated. No student leaves the classroom, and additional students equal to 20 percent of the number of students already seated enter the class late and fill the empty chairs. What is the total number of chairs in the classroom?
(A) 18
(B) 15
(C) 10
(D) 6
(E) 3
Is there a strategic approach to this question? Any experts help please?
At the beginning of a class, a classroom has 3 empty chairs
This topic has expert replies

 Moderator
 Posts: 426
 Joined: Tue Aug 22, 2017 8:48 pm
 Followed by:1 members
GMAT/MBA Expert
 [email protected]
 Elite Legendary Member
 Posts: 10392
 Joined: Sun Jun 23, 2013 6:38 pm
 Location: Palo Alto, CA
 Thanked: 2867 times
 Followed by:511 members
 GMAT Score:800
Hi ardz24,
We're told that at the beginning of a class, a classroom has 3 empty chairs and all students are seated, no student leaves the classroom and an additional number of students equal to 20% of the number of students already seated enter the class late and fill the empty chairs. We're asked for the total number of CHAIRS in the classroom. This question can be solved in a number of different ways, depending on how you choose to do the 'math' involved. Here's how you can TEST THE ANSWERS.
Based on the answer choices  and the fact that the 3 empty chairs represent just 20% of the students who are ALREADY seated  it's likely that one of the larger values is the correct answer. Let's TEST Answer B first....
Answer B = 15 chairs
IF.... there are 15 total chairs...
15  3 = 12 of the chairs are filled
3/12 = 1/4 = 25% of the seats need to be filled. This is TOO HIGH though (it's supposed to be only 20%), so we need to have MORE seats filled. The only way for that to happen is if there were MORE seats to begin with. There's only one answer that matches....
Final Answer: A
GMAT assassins aren't born, they're made,
Rich
We're told that at the beginning of a class, a classroom has 3 empty chairs and all students are seated, no student leaves the classroom and an additional number of students equal to 20% of the number of students already seated enter the class late and fill the empty chairs. We're asked for the total number of CHAIRS in the classroom. This question can be solved in a number of different ways, depending on how you choose to do the 'math' involved. Here's how you can TEST THE ANSWERS.
Based on the answer choices  and the fact that the 3 empty chairs represent just 20% of the students who are ALREADY seated  it's likely that one of the larger values is the correct answer. Let's TEST Answer B first....
Answer B = 15 chairs
IF.... there are 15 total chairs...
15  3 = 12 of the chairs are filled
3/12 = 1/4 = 25% of the seats need to be filled. This is TOO HIGH though (it's supposed to be only 20%), so we need to have MORE seats filled. The only way for that to happen is if there were MORE seats to begin with. There's only one answer that matches....
Final Answer: A
GMAT assassins aren't born, they're made,
Rich
GMAT/MBA Expert
 Brent@GMATPrepNow
 GMAT Instructor
 Posts: 16207
 Joined: Mon Dec 08, 2008 6:26 pm
 Location: Vancouver, BC
 Thanked: 5254 times
 Followed by:1268 members
 GMAT Score:770
Let N = the number of seated students ORIGINALLY in the classardz24 wrote:At the beginning of a class, a classroom has 3 empty chairs and all students are seated. No student leaves the classroom, and additional students equal to 20 percent of the number of students already seated enter the class late and fill the empty chairs. What is the total number of chairs in the classroom?
(A) 18
(B) 15
(C) 10
(D) 6
(E) 3
We're told that the LATE student fill the 3 remaining seats.
So, there are 3 LATE students
We're also told that number of LATE students = 20 percent of the number of students already seated
In other words: number of LATE students = 20 percent of N
Or we can write: 3 = 0.2 N
So, N = 3/0.2 = 15
So, ORIGINALLY, there were 15 seated students AND 3 empty chairs
So, TOTAL number of chairs = 15 + 3 = 18
Answer: A
Cheers,
Brent
GMAT/MBA Expert
 Scott@TargetTestPrep
 GMAT Instructor
 Posts: 7436
 Joined: Sat Apr 25, 2015 10:56 am
 Location: Los Angeles, CA
 Thanked: 43 times
 Followed by:29 members
We can let n = the total number of students who are already seated, and thus:ardz24 wrote:At the beginning of a class, a classroom has 3 empty chairs and all students are seated. No student leaves the classroom, and additional students equal to 20 percent of the number of students already seated enter the class late and fill the empty chairs. What is the total number of chairs in the classroom?
(A) 18
(B) 15
(C) 10
(D) 6
(E) 3
0.2n = 3
n = 15
So, there are 15 + 3 = 18 total chairs.
Answer: A
Scott WoodburyStewart
Founder and CEO
[email protected]
See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

 Legendary Member
 Posts: 2214
 Joined: Fri Mar 02, 2018 2:22 pm
 Followed by:5 members
Let the total number of students seated initially be 'x' and let the total number of chairs in the classroom be 'n'.
$$n=x+3$$
The three empty chairs were filled by 20% of x
$$therefore,\ 20\%\ of\ x=3$$
or 0.2x=3
x=3/0.2=15
this means that 15 students initially occupied 15 seats and the total number of chairs , n, equals to
n=x+3=15+3=18
option A is correct
$$n=x+3$$
The three empty chairs were filled by 20% of x
$$therefore,\ 20\%\ of\ x=3$$
or 0.2x=3
x=3/0.2=15
this means that 15 students initially occupied 15 seats and the total number of chairs , n, equals to
n=x+3=15+3=18
option A is correct

 Senior  Next Rank: 100 Posts
 Posts: 94
 Joined: Tue Dec 16, 2014 9:50 am
 Location: London, UK
 Thanked: 2 times
 Followed by:4 members
 GMAT Score:770
Total Chairs (TC) = Occupied Chairs (OC) + Unoccupied Chairs (UC)ardz24 wrote:At the beginning of a class, a classroom has 3 empty chairs and all students are seated. No student leaves the classroom, and additional students equal to 20 percent of the number of students already seated enter the class late and fill the empty chairs. What is the total number of chairs in the classroom?
(A) 18
(B) 15
(C) 10
(D) 6
(E) 3
Is there a strategic approach to this question? Any experts help please?
(1) UC = 3
(2) UC = 0.2*OC
Put UC from (1) into (2):
3 = 0.2*OC
OC = 15
TC = 15 + 3 = 18
 GMATGuruNY
 GMAT Instructor
 Posts: 15539
 Joined: Tue May 25, 2010 12:04 pm
 Location: New York, NY
 Thanked: 13060 times
 Followed by:1906 members
 GMAT Score:790
We can PLUG IN THE ANSWERS, which represent the number of chairs.ardz24 wrote:At the beginning of a class, a classroom has 3 empty chairs and all students are seated. No student leaves the classroom, and additional students equal to 20 percent of the number of students already seated enter the class late and fill the empty chairs. What is the total number of chairs in the classroom?
(A) 18
(B) 15
(C) 10
(D) 6
(E) 3
Since there are 3 empty chairs at the beginning of class, the original number of students is 3 less than the correct answer choice.
Since the original number of students increases by 20% = 1/5, the original number of students must be a positive MULTIPLE OF 5.
Implication:
When 3 is subtracted from the correct answer choice, the resulting value for the original number of students must be a positive multiple of 5.
Only A works:
183 = 15, which is a positive multiple of 5.
The correct answer is A.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 testtakers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia  a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua  a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Followed here and elsewhere by over 1900 testtakers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia  a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua  a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3