Find all School-related info fast with the new School-Specific MBA Forum

It is currently 22 Oct 2014, 19:12

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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

A and B working together can finish a job in d days. If A

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Director
Director
User avatar
Joined: 26 Feb 2006
Posts: 907
Followers: 4

Kudos [?]: 44 [0], given: 0

A and B working together can finish a job in d days. If A [#permalink] New post 14 Jul 2007, 17:58
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

79% (03:32) correct 21% (02:30) wrong based on 190 sessions
A and B working together can finish a job in d days. If A works alone and completes the job, he will take d + 5 days. If B works alone and completes the same job, he will take d + 45 days. What is d?

A. 25
B. 60
C. 15
D. 14
E. 13

Please solve it with your intellectual prowess!
[Reveal] Spoiler: OA

Last edited by Bunuel on 15 Apr 2012, 23:35, edited 2 times in total.
Edited the question and added the OA
Manager
Manager
avatar
Joined: 12 Feb 2012
Posts: 108
Followers: 1

Kudos [?]: 10 [0], given: 28

Re: A and B working together can finish a job in d days. If A [#permalink] New post 15 Apr 2012, 17:29
Sorry to revisit an old post but this was a toughy! Its not a necessary condition that d be an integer.

So working together they can do the job is d days.
Let r_1 be the rate of A
Let r_2 be the rate of B

Working together their rates to do the job is
Equation1:
(r_1+r_2)d=1 (job)

A working alone can do the job by
Equation2:
(r_1)(d+5)=1 (job)

B working alone can do the job by
Equation3:
(r_2)(d+45)=1 (job)

Now set the first equation to the second equation

(r_1+r_2)d=1 = (r_1)(d+5) solve for d to get d=5(r_1/r_2)

Now set equation1 to equation2

(r_1)(d+5)=1 =(r_2)(d+45) solve to get r_1/r_2=(d+45)/(d+5)

Now substitute d=5(r_1/r_2)=5((d+45)/(d+5))

to get d(d+5)=5(d+45)

which leads you to d^2=5*45. Which is equal to d=15 when you square root both sides (of couse d must be positive, were talking about days here!).

Again, tough problem. If anyone has an easier method let us know.

Last edited by alphabeta1234 on 15 Apr 2012, 17:39, edited 1 time in total.
2 KUDOS received
Senior Manager
Senior Manager
avatar
Joined: 12 Mar 2012
Posts: 370
Concentration: Operations, Strategy
Followers: 2

Kudos [?]: 107 [2] , given: 31

Re: A and B working together can finish a job in d days. If A [#permalink] New post 15 Apr 2012, 17:36
2
This post received
KUDOS
Himalayan wrote:
A and B working together can finish a job in d days. If A works alone and completes the job, he will take d + 5 days. If B works alone and completes the same job, he will take d + 45 days. What is d?

(1) 25
(2) 60
(3) 15
(4) 14
(5) 13

Please solve it with your intellectual prowess!


1/(d+5) +1/(d+45)= 1/d
=> (2d+50)d = (d+5)*(d+45)
=> d^2 = 9*5*5
=> d= 15

hence option C.
_________________

Practice Practice and practice...!!

If my reply /analysis is helpful-->please press KUDOS
If there's a loophole in my analysis--> suggest measures to make it airtight.

Manager
Manager
avatar
Status: I will not stop until i realise my goal which is my dream too
Joined: 25 Feb 2010
Posts: 235
Schools: Johnson '15
Followers: 2

Kudos [?]: 23 [0], given: 16

Re: A and B working together can finish a job in d days. If A [#permalink] New post 15 Apr 2012, 20:40
Himalayan wrote:
A and B working together can finish a job in d days. If A works alone and completes the job, he will take d + 5 days. If B works alone and completes the same job, he will take d + 45 days. What is d?

(1) 25
(2) 60
(3) 15
(4) 14
(5) 13

Please solve it with your intellectual prowess!


take the total work as X

so both A & B can do it in d days, A alone in d+5 and B alone in d+45

rate calculation is total rate = sum of individual rates

X/d = X/(d+5) + X/(d+45)

we can remove X, then the equation becomes as below

1/d = 1/(d+5) + 1/(d+45)

simplification leads to

d^2 = 225

d= + or - 15

u cannot have days in negative right as it should take some time to do a task...hence 15 is the answer...

Note: Give me kudos if my approach is right , else help me understand where i am missing.. I want to bell the GMAT Cat ;)
_________________

Regards,
Harsha

Note: Give me kudos if my approach is right , else help me understand where i am missing.. I want to bell the GMAT Cat ;)

Satyameva Jayate - Truth alone triumphs

Expert Post
3 KUDOS received
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 23381
Followers: 3607

Kudos [?]: 28803 [3] , given: 2849

Re: A and B working together can finish a job in d days. If A [#permalink] New post 15 Apr 2012, 23:36
3
This post received
KUDOS
Expert's post
Himalayan wrote:
A and B working together can finish a job in d days. If A works alone and completes the job, he will take d + 5 days. If B works alone and completes the same job, he will take d + 45 days. What is d?

(1) 25
(2) 60
(3) 15
(4) 14
(5) 13

Please solve it with your intellectual prowess!


If A works alone and completes the job, he will take d + 5 days --> the rate of A is \frac{1}{d+5} job/day;
If B works alone and completes the job, he will take d + 45 days --> the rate of B is \frac{1}{d+45} job/day;

Since A and B working together can finish a job in d days, then their combined rate is \frac{1}{d} job/day;

So, \frac{1}{d+5}+\frac{1}{d+45}=\frac{1}{d}. At this point it's MUCH better to substitute the values from the answer choices rather than to solve for d.

Answer choice C fits: \frac{1}{15+5}+\frac{1}{15+45}=\frac{1}{20}+\frac{1}{60}=\frac{1}{15}.

Answer: C.
_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

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?
25 extra-hard Quant Tests

Get the best GMAT Prep Resources with GMAT Club Premium Membership

Manager
Manager
avatar
Joined: 28 Aug 2012
Posts: 52
Concentration: Operations, Marketing
GMAT 1: 510 Q36 V25
GPA: 4
WE: Information Technology (Other)
Followers: 0

Kudos [?]: 51 [0], given: 105

Re: A and B working together can finish a job in d days. If A [#permalink] New post 25 Dec 2012, 20:21
1
This post was
BOOKMARKED
There is always a trick to such Qs when your given A+B= x days , A= x+ something , B=x+ something .
To find X , use the formula X=\sqrt{ab}

X=\sqrt{5*45}
X= 15 days 8-)

Answer : [C]
Senior Manager
Senior Manager
avatar
Joined: 22 Nov 2010
Posts: 293
Location: India
GMAT 1: 670 Q49 V33
WE: Consulting (Telecommunications)
Followers: 5

Kudos [?]: 29 [0], given: 75

Re: A and B working together can finish a job in d days. If A [#permalink] New post 23 Jan 2013, 22:56
thinktank wrote:
There is always a trick to such Qs when your given A+B= x days , A= x+ something , B=x+ something .
To find X , use the formula X=\sqrt{ab}

X=\sqrt{5*45}
X= 15 days 8-)

Answer : [C]


What is the source of this trick? good one though.it can reduce the time to ans tremendously
_________________

YOU CAN, IF YOU THINK YOU CAN

Manager
Manager
avatar
Joined: 28 Aug 2012
Posts: 52
Concentration: Operations, Marketing
GMAT 1: 510 Q36 V25
GPA: 4
WE: Information Technology (Other)
Followers: 0

Kudos [?]: 51 [0], given: 105

Re: A and B working together can finish a job in d days. If A [#permalink] New post 24 Jan 2013, 00:47
I was going through this 9th grade math text book to pick up on my basics, found a number of shortcuts there :)
Manager
Manager
avatar
Joined: 18 Oct 2011
Posts: 92
Location: United States
Concentration: Entrepreneurship, Marketing
GMAT Date: 01-30-2013
GPA: 3.3
Followers: 2

Kudos [?]: 24 [0], given: 0

Re: A and B working together can finish a job in d days. If A [#permalink] New post 24 Jan 2013, 11:16
1/A = 1/(d+5)
1/B = 1/(d+45)

therefore... 1/(d+5) + 1/(d+45) = 1/d

When you do the math you end up with d^2 = 225. Therefore, d=15
Manager
Manager
avatar
Joined: 04 Jan 2013
Posts: 82
Followers: 0

Kudos [?]: 6 [0], given: 1

Re: A and B working together can finish a job in d days. If A [#permalink] New post 24 Jan 2013, 12:09
:shock: at bunuel..but solving for d is mathematically correct..then why is it that our answer is C
Expert Post
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 23381
Followers: 3607

Kudos [?]: 28803 [0], given: 2849

Re: A and B working together can finish a job in d days. If A [#permalink] New post 25 Jan 2013, 04:40
Expert's post
Manager
Manager
avatar
Joined: 04 Jan 2013
Posts: 82
Followers: 0

Kudos [?]: 6 [0], given: 1

Re: A and B working together can finish a job in d days. If A [#permalink] New post 25 Jan 2013, 13:41
Ow!wow i now get you..it is still the same whether we solve for d or we plugin the answer choices..the only difference is that plugin method is saving us time:-)
CEO
CEO
User avatar
Joined: 09 Sep 2013
Posts: 2831
Followers: 206

Kudos [?]: 42 [0], given: 0

Premium Member
Re: A and B working together can finish a job in d days. If A [#permalink] New post 17 Jun 2014, 08:59
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

Re: A and B working together can finish a job in d days. If A   [#permalink] 17 Jun 2014, 08:59
    Similar topics Author Replies Last post
Similar
Topics:
16 A and B together can complete one-ninth of a job in a day. SravnaTestPrep 6 24 Jul 2013, 18:25
A and B together can do a piece of work in 72/5 days ; B and jyotsnasarabu 1 08 Oct 2006, 03:37
Working together, A and B can do a job in 6 days. B and C GMATT73 6 29 Oct 2005, 09:21
2 working together printer A and B can finish a job in 24 min. FN 11 06 Oct 2005, 18:23
Working together A and B can do a job in 6 days. B & C gmacvik 6 26 Sep 2005, 18:36
Display posts from previous: Sort by

A and B working together can finish a job in d days. If A

  Question banks Downloads My Bookmarks Reviews Important topics  


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

Powered by phpBB © phpBB Group and phpBB SEO

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®.