GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 19 Jan 2019, 08:46

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.

Close

Request Expert Reply

Confirm Cancel
Events & Promotions in January
PrevNext
SuMoTuWeThFrSa
303112345
6789101112
13141516171819
20212223242526
272829303112
Open Detailed Calendar
  • FREE Quant Workshop by e-GMAT!

     January 20, 2019

     January 20, 2019

     07:00 AM PST

     07:00 AM PST

    Get personalized insights on how to achieve your Target Quant Score.
  • Free GMAT Strategy Webinar

     January 19, 2019

     January 19, 2019

     07:00 AM PST

     09:00 AM PST

    Aiming to score 760+? Attend this FREE session to learn how to Define your GMAT Strategy, Create your Study Plan and Master the Core Skills to excel on the GMAT.

Three workers, A, B, and C, can complete a certain task in 10, 5 and x

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Intern
Intern
avatar
B
Joined: 11 Jan 2019
Posts: 2
CAT Tests
Three workers, A, B, and C, can complete a certain task in 10, 5 and x  [#permalink]

Show Tags

New post 12 Jan 2019, 16:28
Hello I am new to GMAT club, and I am unsure if this is the right place to post this, but I am having trouble with what seems like a simple math problem.

Three workers, A, B, and C, can complete a certain task in 10, 5 and x hours respectively. A starts working alone and 2 hours later B joins. After another 2 hours joins C. After that A, B, and C together complete the task in 15 minutes. What is the value of x ?
Answer Choices:
1
1.25
2
2.5
4

I got the answer 2 through plugging in different possible answers, but I do not understand how 1/4*(1/10+1/5+1/x) gives you this answer without plugging in different possibilities.
Manager
Manager
User avatar
G
Status: Manager
Joined: 27 Oct 2018
Posts: 105
Location: Malaysia
Concentration: Strategy, International Business
GPA: 3.67
WE: Pharmaceuticals (Health Care)
GMAT ToolKit User
Re: Three workers, A, B, and C, can complete a certain task in 10, 5 and x  [#permalink]

Show Tags

New post 13 Jan 2019, 00:37
A (alone) completes the task in 10 hours, so in 1 hour he does 1/10 of the task
B (alone) completes the task in 5 hours, so in 1 hour he does 1/5 of the task
C (alone) completes the task in x hours, so in 1 hour he does 1/x of the task

A and B combined do : 1/10 + 1/5 = 3/10 of the task in 1 hour hour
A, B and C combined do: 1/10 + 1/5 + 1/x = 3/10 + 1/x of the task in one hour

A starts work and works for 2 hours, so he completes 1/10* 2 = 1/5 of the task
Then A & B work for next 2 hours and complete 3/10*2 = 3/5 of the task

Remaining uncompleted part = 1 - (1/5 + 3/5) = 1/5
This remaining task is done by A, B and C combined in 15 mins.
1/5 = (1/10 + 1/5 + 1/x)*15/60
so x =2
_________________

...Thanks for KUDOS
Image

Intern
Intern
avatar
B
Joined: 24 Nov 2018
Posts: 13
Location: India
Re: Three workers, A, B, and C, can complete a certain task in 10, 5 and x  [#permalink]

Show Tags

New post 13 Jan 2019, 21:33
Pick a multiple of 5 and 10 for easy calculation.
Total work can be 50
The efficiency of a = 50/10= 5
The efficiency of a = 50/5=10
The efficiency of a = 50/x

First hour: only a is working- 5 units of work
Second hour: only a is working- 5 units of work
Third hour: a: 5 units of work b: 10 units of work
Fourth hour: a: 5 units of work b: 10 units of work
Total - 40 units of work done, remaining unit- 50-40=10

10/ 5+10+(50/x)= 15/60
ie: Remaing work / efficency of all = time

25x=50
x= 2
GMAT Club Bot
Re: Three workers, A, B, and C, can complete a certain task in 10, 5 and x &nbs [#permalink] 13 Jan 2019, 21:33
Display posts from previous: Sort by

Three workers, A, B, and C, can complete a certain task in 10, 5 and x

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  

Moderator: souvonik2k



Copyright

GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.