A cistern has a leak which would empty it in 8 hours. A tap is turned : Problem Solving (PS)

My Profile Logout

Test's Subscription Expires:

My Follow Feed Kudos My Error Log

Messages and Replies

Settings Mark All Read

See All

Applicant Notifications

Settings Mark All Read

See All

Global notifications

Settings Mark All Read

See All

A cistern has a leak which would empty it in 8 hours. A tap is turned

Sort by Date

Sort by Kudos

Author

Message

TAGS:

Hide Tags

Math Expert

Joined: 02 Sep 2009

Posts: 53006

A cistern has a leak which would empty it in 8 hours. A tap is turned [#permalink]

Show Tags

30 Jan 2019, 02:15

00:00

Difficulty:

45% (medium)

Question Stats:

67% (02:50) correct

33% (02:17) wrong

based on 30 sessions

HideShow timer Statistics

A cistern has a leak which would empty it in 8 hours. A tap is turned on which admits 6 litres a minute into the cistern and it is now emptied in 12 hours. How many litres does the cistern hold?

A. 7580
B. 7960
C. 8290
D. 8640
E. 8840

Spoiler: OA

_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.

What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

SVP

Joined: 18 Aug 2017

Posts: 1838

Location: India

Concentration: Sustainability, Marketing

GPA: 4

WE: Marketing (Energy and Utilities)

Re: A cistern has a leak which would empty it in 8 hours. A tap is turned [#permalink]

Show Tags

30 Jan 2019, 03:01

Bunuel wrote:

initial rate =1/8
rate after 6 liters per min is been done = 1/12
so combined rate = 1/8-1/12 = 3-2/24 = 1/24
flow rate in hrs = 6* 60 = 360 ltrs per hr
so vol of cistern = 360 *24 = 8640 ltrs
IMO D
_________________

If you liked my solution then please give Kudos. Kudos encourage active discussions.

Intern

Joined: 01 Feb 2018

Posts: 3

GMAT 1: 640 Q48 V30

A cistern has a leak which would empty it in 8 hours. A tap is turned [#permalink]

Show Tags

10 Feb 2019, 08:11

let X be the rate of emptying.
total capacity of cistern = 8x
additional inflow at the rate of 360 l/hr = 12*360 = 4320
total volume emptied = 4320 + 8x

total volume emptied is also equal to 12x

so, 4320 + 8x = 12x
8x=8640

--------------------------------------------------------------------------
Give kudos if you like this solution

Joined: 07 Dec 2014

Posts: 1156

A cistern has a leak which would empty it in 8 hours. A tap is turned [#permalink]

Show Tags

10 Feb 2019, 10:12

Bunuel wrote:

if leak empties cistern in 8 hours,
in 12 hours it empties 1 1/2 cisterns
extra half cistern must come from tap:
6 lpm*60m*12h*2 halves=8640 litres cistern capacity
D