Events & Promotions
|
|
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
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Nov 2007:30 AM PST
-08:30 AM PST
Learn what truly sets the UC Riverside MBA apart and how it helps in your professional growth
Nov 2211:00 AM IST
-01:00 PM IST
Do RC/MSR passages scare you? e-GMAT is conducting a masterclass to help you learn – Learn effective reading strategies Tackle difficult RC & MSR with confidence Excel in timed test environment- Nov 23
11:00 AM IST
-01:00 PM IST
Attend this free GMAT Algebra Webinar and learn how to master the most challenging Inequalities and Absolute Value problems with ease. 
Nov 2510:00 AM EST
-11:00 AM EST
Prefer video-based learning? The Target Test Prep OnDemand course is a one-of-a-kind video masterclass featuring 400 hours of lecture-style teaching by Scott Woodbury-Stewart, founder of Target Test Prep and one of the most accomplished GMAT instructors.
12 Jan 2022, 04:00
Kudos
Bookmarks
A
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
75%
(hard)
Question Stats:
58% (02:25) correct
42%
(02:12)
wrong
based on 213
sessions
History
Date
Time
Result
Not Attempted Yet
Consider 20 identical pipes that supply water to a tank. What is the minimum number of pipes that has to be kept open if one needs to fill the tank within 30 minutes?
(1) When 8 pipes are kept open, the tank gets filled 20 minutes sooner than when 6 pipes are kept open.
(2) If all the 20 pipes are kept open, the tank gets filled in less than 15 minutes.
(1) When 8 pipes are kept open, the tank gets filled 20 minutes sooner than when 6 pipes are kept open.
(2) If all the 20 pipes are kept open, the tank gets filled in less than 15 minutes.
13 Jan 2022, 01:28
Kudos
Bookmarks
1)
Rate for 8 pipes:
\(\frac{8}{x}=\frac{1}{C-20}\)
\(x = 8C - 160\) (1)
Rate for 6 pipes:
\(\frac{6}{x} = \frac{1}{C}\)
\(x = 6C\) (2)
Plugging in (2) into (1):
\(6C = 8C - 160\)
\(2C = 160\)
\(C = 80\)
It takes 6 pipes 80 minutes to fill up the tank and that it takes 8 pipes 60 minutes to fill up the tank, which means that to fill the tank up within 30 minutes it will take 16 pipes.
SUFFICIENT
2)
Does not give us enough information to answer the question as the timeframe could be any number below 15.
INSUFFICIENT
Answer A
Rate for 8 pipes:
\(\frac{8}{x}=\frac{1}{C-20}\)
\(x = 8C - 160\) (1)
Rate for 6 pipes:
\(\frac{6}{x} = \frac{1}{C}\)
\(x = 6C\) (2)
Plugging in (2) into (1):
\(6C = 8C - 160\)
\(2C = 160\)
\(C = 80\)
It takes 6 pipes 80 minutes to fill up the tank and that it takes 8 pipes 60 minutes to fill up the tank, which means that to fill the tank up within 30 minutes it will take 16 pipes.
SUFFICIENT
2)
Does not give us enough information to answer the question as the timeframe could be any number below 15.
INSUFFICIENT
Answer A
28 May 2024, 03:19
Kudos
Bookmarks
Bunuel
Use ratio of work rate discussed here: https://youtu.be/88NFTttkJmA
But note that the question is not correct as per GMAT requirement. The data in the two statements conflicts with each other.
We have 20 identical pipes.
(1) When 8 pipes are kept open, the tank gets filled 20 minutes sooner than when 6 pipes are kept open.
When ratio of rate of work is 8:6 (= 4:3) (since pipes are identical, more pipes open will mean propotionally higher rate of work), the ratio of time taken will be 3:4. The difference of 1 on ratio scale is equal to 20 mins which means that 8 pipes take 60 mins to fill the tank.
So to fill the tank in 30 mins, we need at least 16 pipes open.
Sufficient alone.
(2) If all the 20 pipes are kept open, the tank gets filled in less than 15 minutes.
Less than 15 mins could take many values such as 10 mins or 5 mins and each case will give us a different number of open pipes needed.
e.g.
If 20 pipes take 10 mins, to fill the tank in 30 mins, we need at least 20/3 i.e. 7 pipes open.
If 20 pipes take 5 mins, to fill the tank in 30 mins, we need at least 20/6 i.e. 4 pipes open.
etc.
Not sufficient alone.
(Note that as per statement 1, we would actually need more than 32 pipes to fill the tank in less than 15 mins.)
Answer (A)
