Last visit was: 18 Nov 2025, 19:54 It is currently 18 Nov 2025, 19:54
Home
GMAT
Messages
Tests
Schools
Events
Rewards
Chat
My Profile
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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel
Back to Forum
Create Topic
805+ Level|   Combinations|      
User avatar
sherlocked221B
User avatar
Joined: 30 Jan 2024
Last visit: 23 Sep 2025
Posts: 94
Own Kudos:
69
 [10]
Given Kudos: 344
Location: India
Concentration: Technology, Strategy
Schools: ISB ESADE'26 NUS '26 HEC
GMAT Focus 1: 645 Q87 V80 DI78
GPA: 8.45
WE:Engineering (Consulting)
Products:
My Reviews
Schools: ISB ESADE'26 NUS '26 HEC
GMAT Focus 1: 645 Q87 V80 DI78
Posts: 94
Kudos: 69
 [10]
­In a apartment there are 5 floors each with 4 water taps on each Updated on: 26 Jul 2024, 21:32
Originally posted by sherlocked221B on 20 Jul 2024, 06:43.
Last edited by sherlocked221B on 26 Jul 2024, 21:32, edited 1 time in total.
Kudos
Add Kudos
9
Bookmarks
Bookmark this Post
00:00
Start Timer
Pause Timer
Resume Timer
Show Answer
Hide
Show
History
D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

Difficulty:

95% (hard)

Question Stats:

20% (02:33) correct 80% (03:21) wrong based on 95 sessions

History

Date
Time
Result
Not Attempted Yet
­In a apartment there are 5 floors each with 4 water taps on each floor. Any 2 taps in the same floor are connected with 4 pipes and any 2 taps in different floors are connected with 4 pipes. In one of the floors all the pipes connecting the taps with the taps in the other floors burst and in another floor all the pipes connecting the taps in that floor amongst themselves burst, though all other pipes remain intact. What is the percentage reduction in the number of pipes?

(A) 28
(B) 32
(C) 33
(D) 35
(E) 36­

[Might not be a GMAT Level Question, but I came across a similar one in one of the resources I was following]
[Ambiguous and Difficult]
ShowHide Answer
Official Answer
D
User avatar
Danush649
User avatar
Joined: 26 Apr 2020
Last visit: 12 Nov 2025
Posts: 42
Own Kudos:
28
Given Kudos: 63
Location: India
Schools: HEC Jan'22 Intake
GMAT 1: 720 Q49 V39
Products:
Forum Quiz
Schools: HEC Jan'22 Intake
GMAT 1: 720 Q49 V39
Posts: 42
Kudos: 28
­In a apartment there are 5 floors each with 4 water taps on each 20 Jul 2024, 08:59
Kudos
Add Kudos
Bookmarks
Bookmark this Post
im getting 36
64+6/ 190
User avatar
Natashaairan
User avatar
Joined: 12 May 2024
Last visit: 30 Aug 2025
Posts: 37
Own Kudos:
15
Given Kudos: 15
Location: India
Posts: 37
Kudos: 15
­In a apartment there are 5 floors each with 4 water taps on each 21 Jul 2024, 23:39
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Can somebody please explain
I didn’t get the pipes logic.. how many to consider..

Posted from my mobile device
User avatar
Charleeagni
User avatar
Joined: 26 May 2024
Last visit: 26 Jan 2025
Posts: 3
Own Kudos:
5
 [2]
Given Kudos: 33
Posts: 3
Kudos: 5
 [2]
­In a apartment there are 5 floors each with 4 water taps on each 22 Jul 2024, 05:45
2
Kudos
Add Kudos
Bookmarks
Bookmark this Post
To find the percentage reduction in the number of pipes in the apartment building, we first need to calculate the total number of pipes before and after the bursts.


  1. Total number of taps:


    • There are 5 floors, each with 4 taps.
    • Total taps TT = 5×4=205×4=20 taps.
  2. Pipes connecting taps on the same floor:


    • Each floor has 4 taps.
    • The number of ways to choose 2 taps out of 4 is (42)=6(24​)=6.
    • Each pair of taps is connected by 4 pipes.
    • Pipes per floor = 6×4=246×4=24 pipes.
    • For 5 floors, total pipes on the same floor = 5×24=1205×24=120 pipes.
  3. Pipes connecting taps on different floors:


    • Total taps = 20.
    • The number of ways to choose 2 taps out of 20 is (202)=190(220​)=190.
    • Each pair of taps is connected by 4 pipes.
    • Total pipes between floors = 190×4=760190×4=760 pipes.
  4. Total number of pipes initially:


    • Total pipes = 120120 (same floor) + 760760 (different floors) = 880880 pipes.
Now, we consider the two types of bursts:


  1. Bursting pipes connecting taps between one floor and other floors:


    • Choose any one floor: it has 4 taps.
    • Each of these 4 taps must be connected to each of the other 16 taps (in different floors).
    • Each connection is via 4 pipes.
    • Total burst pipes for this floor = 4×16×4=2564×16×4=256 pipes.
  2. Bursting pipes connecting taps within one floor:


    • Choose any one floor: it has 4 taps.
    • As calculated, the number of pipes connecting these taps = 24 pipes.
  3. Total burst pipes:


    • Total burst pipes = 256256 (between floors) + 2424 (within one floor) = 280280 pipes.
  4. Number of pipes after the bursts:


    • Remaining pipes = Initial pipes - Burst pipes = 880−280=600880−280=600 pipes.
  5. Percentage reduction in the number of pipes:


    • Percentage reduction = Burst pipesInitial pipes×100%InitialpipesBurstpipes​×100%
    • Percentage reduction = 280880×100%≈31.82%880280​×100%≈31.82%
Thus, the percentage reduction in the number of pipes is approximately 31.82%

The closest is 32.
User avatar
Natashaairan
User avatar
Joined: 12 May 2024
Last visit: 30 Aug 2025
Posts: 37
Own Kudos:
15
Given Kudos: 15
Location: India
Posts: 37
Kudos: 15
­In a apartment there are 5 floors each with 4 water taps on each 22 Jul 2024, 07:34
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Charleeagni
To find the percentage reduction in the number of pipes in the apartment building, we first need to calculate the total number of pipes before and after the bursts.


  1. Total number of taps:


    • There are 5 floors, each with 4 taps.
    • Total taps TT = 5×4=205×4=20 taps.
  2. Pipes connecting taps on the same floor:


    • Each floor has 4 taps.
    • The number of ways to choose 2 taps out of 4 is (42)=6(24​)=6.
    • Each pair of taps is connected by 4 pipes.
    • Pipes per floor = 6×4=246×4=24 pipes.
    • For 5 floors, total pipes on the same floor = 5×24=1205×24=120 pipes.
  3. Pipes connecting taps on different floors:


    • Total taps = 20.
    • The number of ways to choose 2 taps out of 20 is (202)=190(220​)=190.
    • Each pair of taps is connected by 4 pipes.
    • Total pipes between floors = 190×4=760190×4=760 pipes.
  4. Total number of pipes initially:


    • Total pipes = 120120 (same floor) + 760760 (different floors) = 880880 pipes.
Now, we consider the two types of bursts:


  1. Bursting pipes connecting taps between one floor and other floors:


    • Choose any one floor: it has 4 taps.
    • Each of these 4 taps must be connected to each of the other 16 taps (in different floors).
    • Each connection is via 4 pipes.
    • Total burst pipes for this floor = 4×16×4=2564×16×4=256 pipes.
  2. Bursting pipes connecting taps within one floor:


    • Choose any one floor: it has 4 taps.
    • As calculated, the number of pipes connecting these taps = 24 pipes.
  3. Total burst pipes:


    • Total burst pipes = 256256 (between floors) + 2424 (within one floor) = 280280 pipes.
  4. Number of pipes after the bursts:


    • Remaining pipes = Initial pipes - Burst pipes = 880−280=600880−280=600 pipes.
  5. Percentage reduction in the number of pipes:


    • Percentage reduction = Burst pipesInitial pipes×100%InitialpipesBurstpipes​×100%
    • Percentage reduction = 280880×100%≈31.82%880280​×100%≈31.82%
Thus, the percentage reduction in the number of pipes is approximately 31.82%

The closest is 32.
Show more


Your answer is not matching

Posted from my mobile device
User avatar
TheVDR
User avatar
Joined: 09 Jun 2023
Last visit: 05 Nov 2025
Posts: 254
Own Kudos:
224
Given Kudos: 20
Location: India
Posts: 254
Kudos: 224
­In a apartment there are 5 floors each with 4 water taps on each 23 Jul 2024, 01:31
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Quote:
any 2 taps in different floors are connected with 4 pipes.
Show more
This has ambiguous and has multiple meanings. There can be combinations of 2 taps, on from different floor, each connected with 4 pipes, making a total of 20 pipes. It is also possible that each tap is connected to some other tap of all other floors, making a total of 9! * 4 pipes. Neither is giving a 35% reduction (as the OA is D)

­
User avatar
Regor60
User avatar
Joined: 21 Nov 2021
Last visit: 17 Nov 2025
Posts: 528
Own Kudos:
383
 [1]
Given Kudos: 459
Posts: 528
Kudos: 383
 [1]
­In a apartment there are 5 floors each with 4 water taps on each 24 Jul 2024, 12:31
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Not a good question due to ambiguous description of the layout.

Posted from my mobile device
User avatar
aryamanchadha
User avatar
Joined: 17 Jan 2024
Last visit: 07 Jul 2025
Posts: 1
Given Kudos: 2
Posts: 1
Kudos: 0
­In a apartment there are 5 floors each with 4 water taps on each 24 Jul 2024, 22:28
Kudos
Add Kudos
Bookmarks
Bookmark this Post
­4 pipes connecting any 2 pipes on one floor - As there are 6 lines (sides and diagonals) that connect all 4 taps on one floor.
As each line has 4 pipes, pipes connecting taps on one floor = 6*4 = 24
Total Pipes connecting taps on their own floor = 5*24 = 120.

4 pipes connecting any 2 taps on any two floors - Lets calculate how many connections are there between 2 floors.

As each tap connects to the 4 taps above it, there are 4 lines running from each tap to the floor above.
Each line is 4 pipes => each tap has 16 pipes running to each floor.
pipes running out to one floor from another floor = 4 * pipes running from one tap to each floor.
Pipes running from one floor to another floor = 4 * 16 = 64.

Total pipes running between floors (not on the same floor) = 64*4 + 64*3 + 64*2 + 64*1 = 64*(4+3+2+1) = 64*11 = 704
(first floor will connect to the other 4 floors and the second floor will connect to the 3 above it as the connections going down are already counted.)

Total Pipes = 704 + 120 = 824

Pipes burst on one floor = 24 (all the pipes)

Pipes burst goint to another floor = 64*4 = 256 (64 pipes each going to the other 4 floors)

Total Pipes burst = 256+24 = 280.

%pipes burst = (280/824) * 100 = 33.9%

Rounded off to 34 I guess but still not 35 :/

Please tell me where I messed up
User avatar
Maydey23
User avatar
Joined: 05 Mar 2024
Last visit: 19 Jun 2025
Posts: 2
Own Kudos:
1
Given Kudos: 1
Location: India
Posts: 2
Kudos: 1
­In a apartment there are 5 floors each with 4 water taps on each 10 Feb 2025, 02:09
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Charleeagni
To find the percentage reduction in the number of pipes in the apartment building, we first need to calculate the total number of pipes before and after the bursts.


  1. Total number of taps:


    • There are 5 floors, each with 4 taps.
    • Total taps TT = 5×4=205×4=20 taps.
  2. Pipes connecting taps on the same floor:


    • Each floor has 4 taps.
    • The number of ways to choose 2 taps out of 4 is (42)=6(24)=6.
    • Each pair of taps is connected by 4 pipes.
    • Pipes per floor = 6×4=246×4=24 pipes.
    • For 5 floors, total pipes on the same floor = 5×24=1205×24=120 pipes.
  3. Pipes connecting taps on different floors:


    • Total taps = 20.
    • The number of ways to choose 2 taps out of 20 is (202)=190(220)=190.
    • Each pair of taps is connected by 4 pipes.
    • Total pipes between floors = 190×4=760190×4=760 pipes.
  4. Total number of pipes initially:


    • Total pipes = 120120 (same floor) + 760760 (different floors) = 880880 pipes.
Now, we consider the two types of bursts:


  1. Bursting pipes connecting taps between one floor and other floors:


    • Choose any one floor: it has 4 taps.
    • Each of these 4 taps must be connected to each of the other 16 taps (in different floors).
    • Each connection is via 4 pipes.
    • Total burst pipes for this floor = 4×16×4=2564×16×4=256 pipes.
  2. Bursting pipes connecting taps within one floor:


    • Choose any one floor: it has 4 taps.
    • As calculated, the number of pipes connecting these taps = 24 pipes.
  3. Total burst pipes:


    • Total burst pipes = 256256 (between floors) + 2424 (within one floor) = 280280 pipes.
  4. Number of pipes after the bursts:


    • Remaining pipes = Initial pipes - Burst pipes = 880−280=600880−280=600 pipes.
  5. Percentage reduction in the number of pipes:


    • Percentage reduction = Burst pipesInitial pipes×100%InitialpipesBurstpipes×100%
    • Percentage reduction = 280880×100%≈31.82%880280×100%≈31.82%
Thus, the percentage reduction in the number of pipes is approximately 31.82%

The closest is 32.
Show more
Also, since we're picking any two taps between all floors, won't there be an overlap of the same floor taps?
User avatar
Maydey23
User avatar
Joined: 05 Mar 2024
Last visit: 19 Jun 2025
Posts: 2
Own Kudos:
1
 [1]
Given Kudos: 1
Location: India
Posts: 2
Kudos: 1
 [1]
­In a apartment there are 5 floors each with 4 water taps on each 25 Feb 2025, 03:54
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
sherlocked221B
­In a apartment there are 5 floors each with 4 water taps on each floor. Any 2 taps in the same floor are connected with 4 pipes and any 2 taps in different floors are connected with 4 pipes. In one of the floors all the pipes connecting the taps with the taps in the other floors burst and in another floor all the pipes connecting the taps in that floor amongst themselves burst, though all other pipes remain intact. What is the percentage reduction in the number of pipes?

(A) 28
(B) 32
(C) 33
(D) 35
(E) 36­

[Might not be a GMAT Level Question, but I came across a similar one in one of the resources I was following]
[Ambiguous and Difficult]
Show more
Here's how I got the solution.

Same floor - total pipes between 4 taps = 24
Total same floor pipes across 5 floors = 24×5 = 120

Now, for seperate floors.
Each tap is connected to any other tap on any floor via 4 pipes.
So, any tap on floor one is connected to 16 other taps via 4 pipes , hence pipe count for floor
1 =16*4*4
Each tap on Floor 2 is connected to 12 other taps - 12*4*4 ( it's connection with first floor taps have already been counted)
Total pipes ( seperate floors) = 16*4*4+12*4*4+8*4*4+16*4 = 640

Total pipes combined = 120+640= 760

Pipes burst = 24 + 256 = 280

% reduction in pipes = 280/760*100 ---> 7/19*100 (rounding off the 19 to 20) -----> 700/20 = 35%
Moderators:
Bunuel
Math Expert
105355 posts
Krunaal
Tuck School Moderator
805 posts