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

It is currently 27 Aug 2014, 07:06

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

re: help !

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Intern
Intern
avatar
Joined: 02 Jul 2009
Posts: 16
Followers: 0

Kudos [?]: 1 [0], given: 12

re: help ! [#permalink] New post 10 Jul 2009, 13:32
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
could some one tell me the formula for ansewring this question?

If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

A. 2 hours and 24 minutes
B. 3 hours and 12 minutes
C. 3 hours and 44 minutes
D. 4 hours and 10 minutes
E. 4 hours and 33 minutes
Expert Post
Founder
Founder
User avatar
Affiliations: UA-1K, SPG-G, HH-D
Joined: 04 Dec 2002
Posts: 12077
Location: United States (WA)
GMAT 1: 750 Q49 V42
GPA: 3.5
WE: Information Technology (Hospitality and Tourism)
Followers: 2229

Kudos [?]: 8333 [0], given: 3643

GMAT ToolKit User Premium Member CAT Tests
Re: re: help ! [#permalink] New post 10 Jul 2009, 13:39
Expert's post
Moved to the appropriate Forum
_________________

Founder of GMAT Club

Just starting out with GMAT? Start here... | Want to know your GMAT Score? Try GMAT Score Estimator
Need GMAT Book Recommendations? Best GMAT Books

Co-author of the GMAT Club tests

Have a blog? Feature it on GMAT Club!

Get the best GMAT Prep Resources with GMAT Club Premium Membership

1 KUDOS received
Senior Manager
Senior Manager
avatar
Joined: 16 Apr 2009
Posts: 251
Schools: Ross
Followers: 1

Kudos [?]: 21 [1] , given: 10

GMAT Tests User
Re: re: help ! [#permalink] New post 10 Jul 2009, 14:08
1
This post received
KUDOS
Quote:
If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, how long will it take for both of them to paint the house together?

A. 2 hours and 24 minutes
B. 3 hours and 12 minutes
C. 3 hours and 44 minutes
D. 4 hours and 10 minutes
E. 4 hours and 33 minutes


Sally -a house in 4 hrs
1 hr -1/4

John -a house in 6 hrs
1 hr -1/6

Together sally and John in one hour complete
1/4+1/6 =6+4/24=10/24 =5/12


1 hr - 5/12 part of the house
? hr - whole house

Whole house = 12/5 =2 hrs 24 min
_________________

Keep trying no matter how hard it seems, it will get easier.

1 KUDOS received
Senior Manager
Senior Manager
avatar
Joined: 25 Mar 2009
Posts: 305
Followers: 6

Kudos [?]: 66 [1] , given: 6

GMAT Tests User
Re: re: help ! [#permalink] New post 10 Jul 2009, 14:09
1
This post received
KUDOS
Someone please correct me if I'm wrong. I'm a little rusty with rate/work problems.

Know this formula: R*T = W (Rate)*(Time) = Work

Sally: Rate * 4 hours = 1 house
Rate = 1/4

John: Rate * 6 hours = 1 house
Rate = 1/6

Working together, you combine their rates. So working together, their rate is: 1/4 + 1/6 = 10/24

So go back to the original equation R*T = W and make a new one with this new information. What do we know? Their rate is 10/24 houses/hour. They are going to paint 1 house (this is W). We need to find the time it takes (T). So we have:

(10/24)*T = 1
T = 24/10 = 12/5 hours

This is 2 and 2/5 hours. 2/5 of one hour is 24 min. So it will take 2 hours and 24 min. Answer A.

Also note that you can immediately eliminate answer choices D and E because Sally takes only 4 hours to paint a house. If John helps, no matter how slow/fast he paints, it will take less than 4 hours.
1 KUDOS received
Senior Manager
Senior Manager
avatar
Joined: 04 Jun 2008
Posts: 306
Followers: 5

Kudos [?]: 97 [1] , given: 15

GMAT Tests User
Re: re: help ! [#permalink] New post 10 Jul 2009, 14:49
1
This post received
KUDOS
wud just like to contribute a simpler method which i found very useful in doing faster calculations.

this method works for all "rate of doing work" problems, including distance and speed.

When rate of work is given, we usually have to calculate using reciprocals. instead take the lcm of all the rates of work of different people.
ie, here 4 hrs and 6 hrs,,,,,, lcm = 12

consider this lcm to be the total units of work to be done, ie, 12 units to be painted

Then, sally can paint the 12 units in 4 hours, or per hour she paints 3 units.
John paints 12 in 6 hours, so per hour he paints 12/6 = 2 units

Now both working together will paint 3+2 = 5 units per hour

To paint 5 units they take 1 hour, so to paint 12 units they will take 12/5 hours.

This method is excellent for doing simple calculations mentally. No need to use pen and paper. Try applying it to all time and work or speed and distance problems while practicing.
Intern
Intern
avatar
Joined: 11 Jul 2009
Posts: 15
Followers: 0

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

Re: re: help ! [#permalink] New post 11 Jul 2009, 09:24
Nice one rashmine. Very sensible method.

I worked it out in normal way to get 12/5.

thanks
Intern
Intern
avatar
Joined: 05 Sep 2006
Posts: 17
Followers: 0

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

Re: re: help ! [#permalink] New post 13 Jul 2009, 11:18
I worked it out the normal way as well and got confused by 12/5 = 2.4 so 2 hours and 40% of 60 minutes.. Is there is way not to confuse when converting the decimals to hours and minutes ?
Senior Manager
Senior Manager
User avatar
Joined: 20 Mar 2008
Posts: 455
Followers: 1

Kudos [?]: 67 [0], given: 5

GMAT Tests User
Re: re: help ! [#permalink] New post 13 Jul 2009, 12:41
parimal wrote:
I worked it out the normal way as well and got confused by 12/5 = 2.4 so 2 hours and 40% of 60 minutes.. Is there is way not to confuse when converting the decimals to hours and minutes ?


Donno if this helps, but I try to avoid using decimals when working with hr & minutes.

What I try to do is write the number as 2 2/5, however you still have to remember that 2/5 is of 60, not 100.
Re: re: help !   [#permalink] 13 Jul 2009, 12:41
    Similar topics Author Replies Last post
Similar
Topics:
Experts publish their posts in the topic Help for Re-attempt bsahil 2 25 Aug 2013, 22:19
RE: GMAT - Need Help smooveal 1 05 Aug 2011, 15:56
Re: Integer help! BenchPrepGURU 6 29 Jul 2011, 12:25
Re-applying strategy ! (please help) samdee 5 22 Dec 2006, 17:25
Re-applying strategy ! (please help) samdee 2 22 Dec 2006, 17:24
Display posts from previous: Sort by

re: help !

  Question banks Downloads My Bookmarks Reviews Important topics  


cron

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®.