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

It is currently 13 Oct 2019, 18:05

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

When working together at their constant rates, machines A and B can

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Find Similar Topics 
Senior Manager
Senior Manager
User avatar
P
Joined: 15 Feb 2018
Posts: 365
Premium Member
When working together at their constant rates, machines A and B can  [#permalink]

Show Tags

New post 13 Oct 2018, 05:41
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

79% (00:57) correct 21% (01:30) wrong based on 64 sessions

HideShow timer Statistics

When working together at their constant rates, machines A and B can complete a certain task in 4 hours. How many hours would it take machine B to complete the task, when working alone at its constant rate?

1) When working alone at its constant rate, machine A can finish the task in 6 hours.

2) When working alone at their respective rates, it takes machine B 6 hours longer than machine A to finish the task
Director
Director
avatar
G
Joined: 19 Oct 2013
Posts: 520
Location: Kuwait
GPA: 3.2
WE: Engineering (Real Estate)
GMAT ToolKit User
Re: When working together at their constant rates, machines A and B can  [#permalink]

Show Tags

New post 13 Oct 2018, 06:19
1
1
philipssonicare wrote:
When working together at their constant rates, machines A and B can complete a certain task in 4 hours. How many hours would it take machine B to complete the task, when working alone at its constant rate?

1) When working alone at its constant rate, machine A can finish the task in 6 hours.

2) When working alone at their respective rates, it takes machine B 6 hours longer than machine A to finish the task


1/A + 1/B = (A+B)/A*B

This the combined rate 1 job in 4 hours

So it means 4 hours to finish 1 job.

We want to know B

Statement 1)

Tells us that 1/6 + 1/B = 1/4

1/4 - 1/6 = 1/B sufficient.

3/12 - 2/12 = 1/12. B takes 12 hours.


Statement 2)

1/A + 1/(A+6) = 1/4

We can find the value of A and therefore find the value of B.

Sufficient.

(A + A + 6)/(A^2 + 6A) = 1/4

4A + 4A + 24 = A^2 + 6A

A^2 - 2A - 24 = 0

(A - 6) (A + 4) = 0

A = 6
B = 12

Answer choice D

Posted from my mobile device
GMAT Club Bot
Re: When working together at their constant rates, machines A and B can   [#permalink] 13 Oct 2018, 06:19
Display posts from previous: Sort by

When working together at their constant rates, machines A and B can

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





cron

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