BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

How many students?

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 107
Joined: Sat Feb 27, 2010 11:10 am
GMAT Score:690

How many students?

by singhsa » Mon Sep 20, 2010 11:43 pm
How many different ways can 2 students be seated in a row of 4 desks, so that there is always at least one empty desk between the students?
A. 2
B. 3
C. 4
D. 6
E. 12

Came across this question and could easily solve it by taking students as A and B. But is there a formula used in this sort of question in case the nos are more complex? Thnx

Oh, BTW, OA - 6
Top
Source: — Problem Solving |
User avatar
GMAT Instructor
Posts: 3650
Joined: Wed Jan 21, 2009 4:27 am
Location: India
Thanked: 267 times
Followed by:80 members
GMAT Score:760

by sanju09 » Tue Sep 21, 2010 12:13 am
singhsa wrote:How many different ways can 2 students be seated in a row of 4 desks, so that there is always at least one empty desk between the students?
A. 2
B. 3
C. 4
D. 6
E. 12

Came across this question and could easily solve it by taking students as A and B. But is there a formula used in this sort of question in case the nos are more complex? Thnx

Oh, BTW, OA - 6

We need to select 3 desks in a row, out of the four desks, so that there is only one empty desk between the students. This can be done in 2 ways only. Or, we select all four desks, so that there are at max 2 empty desks between the students. This can be done in just 1 way. The ways add up to 3, and the two fellows may again be arranged in 2! = 2 ways, within their desks. The many different ways would then sum up to [spoiler]3 × 2 = 6.

D[/spoiler]

No, there's no formula designed for tailored or fragmented distribution of elements.
The mind is everything. What you think you become. -Lord Buddha



Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com
Top
Master | Next Rank: 500 Posts
Posts: 107
Joined: Sat Feb 27, 2010 11:10 am
GMAT Score:690

by singhsa » Tue Sep 21, 2010 12:33 am
sanju09 wrote:
singhsa wrote:How many different ways can 2 students be seated in a row of 4 desks, so that there is always at least one empty desk between the students?
A. 2
B. 3
C. 4
D. 6
E. 12

Came across this question and could easily solve it by taking students as A and B. But is there a formula used in this sort of question in case the nos are more complex? Thnx

Oh, BTW, OA - 6

We need to select 3 desks in a row, out of the four desks, so that there is only one empty desk between the students. This can be done in 2 ways only. Or, we select all four desks, so that there are at max 2 empty desks between the students. This can be done in just 1 way. The ways add up to 3, and the two fellows may again be arranged in 2! = 2 ways, within their desks. The many different ways would then sum up to [spoiler]3 × 2 = 6.

D[/spoiler]

No, there's no formula designed for tailored or fragmented distribution of elements.
Hey, thnx. I get the concept now, but what if in the GMAT, the question asks us to arrange 3 students in a row of 10 desks in a similar manner as the question above? It'll be tedious solving the question this way.
Top
User avatar
GMAT Instructor
Posts: 3650
Joined: Wed Jan 21, 2009 4:27 am
Location: India
Thanked: 267 times
Followed by:80 members
GMAT Score:760

by sanju09 » Tue Sep 21, 2010 1:51 am
singhsa wrote:
sanju09 wrote:
singhsa wrote:How many different ways can 2 students be seated in a row of 4 desks, so that there is always at least one empty desk between the students?
A. 2
B. 3
C. 4
D. 6
E. 12

Came across this question and could easily solve it by taking students as A and B. But is there a formula used in this sort of question in case the nos are more complex? Thnx

Oh, BTW, OA - 6

We need to select 3 desks in a row, out of the four desks, so that there is only one empty desk between the students. This can be done in 2 ways only. Or, we select all four desks, so that there are at max 2 empty desks between the students. This can be done in just 1 way. The ways add up to 3, and the two fellows may again be arranged in 2! = 2 ways, within their desks. The many different ways would then sum up to [spoiler]3 × 2 = 6.

D[/spoiler]

No, there's no formula designed for tailored or fragmented distribution of elements.
Hey, thnx. I get the concept now, but what if in the GMAT, the question asks us to arrange 3 students in a row of 10 desks in a similar manner as the question above? It'll be tedious solving the question this way.
hope nice things of GMAT please
The mind is everything. What you think you become. -Lord Buddha



Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com
Top
Post new topic Post Reply
• Page 1 of 1