• NEW! FREE Beat The GMAT Quizzes
Hundreds of Questions Highly Detailed Reporting Expert Explanations
• 7 CATs FREE!
If you earn 100 Forum Points

Engage in the Beat The GMAT forums to earn
100 points for $49 worth of Veritas practice GMATs FREE VERITAS PRACTICE GMAT EXAMS Earn 10 Points Per Post Earn 10 Points Per Thanks Earn 10 Points Per Upvote ## A conference room ##### This topic has 2 expert replies and 0 member replies ### Top Member ## A conference room A conference room has two analog (12-hour format) clocks, one on the north wall and one on the south wall. The clock on the north wall loses 30 seconds per hour, and the clock on the south wall gains 15 seconds per hour. If the clocks begin displaying the same time, after how long will they next display the same time again? A. 32 days B. 36 days C. 40 days D. 44 days E. 48 days Can some experts show me the best solution in this problem? How will i start solving it? OA C ### GMAT/MBA Expert GMAT Instructor Joined 09 Apr 2015 Posted: 1465 messages Followed by: 19 members Upvotes: 39 Top Reply lheiannie07 wrote: A conference room has two analog (12-hour format) clocks, one on the north wall and one on the south wall. The clock on the north wall loses 30 seconds per hour, and the clock on the south wall gains 15 seconds per hour. If the clocks begin displaying the same time, after how long will they next display the same time again? A. 32 days B. 36 days C. 40 days D. 44 days E. 48 days We can see that the clock on the north wall loses twice as much time as the clock on the south wall gains. We can assume the time that both clocks display is 12 oâ€™clock, i.e., the hour hand is on the number 12 on both clocks. The next time they will display the same time is 4 oâ€™clock, since the clock on the south wall gains 4 hours and the clock on the north wall loses 8 hours. From the south clock point of view: Since 4 hours = 4 x 3600 = 14400 seconds and the clock on the south wall gains 15 seconds per hour, it needs 14400/15 = 960 hours or 40 days to strike 4 oâ€™clock as the clock on the north wall strikes the same time. Or, from the north clock point of view: Since 8 hours = 8 x 3600 = 28800 seconds and the clock on the north wall loses 30 seconds per hour, it needs 28800/30 = 960 hours or 40 days to strike 4 oâ€™clock as the clock on the south wall strikes the same time. In either case, the number of days needed is 40. Answer: C _________________ Jeffrey Miller Head of GMAT Instruction jeff@targettestprep.com See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews ### GMAT/MBA Expert GMAT Instructor Joined 04 Oct 2017 Posted: 551 messages Followed by: 11 members Upvotes: 180 Top Reply Quote: A conference room has two analog (12-hour format) clocks, one on the north wall and one on the south wall. The clock on the north wall loses 30 seconds per hour, and the clock on the south wall gains 15 seconds per hour. If the clocks begin displaying the same time, after how long will they next display the same time again? A. 32 days B. 36 days C. 40 days D. 44 days E. 48 days Can some experts show me the best solution in this problem? How will i start solving it? OA C Hi lheiannie07, Let's take a look at your question. The North clock loses 30 sec/hr and the South clock gains 15 sec/hr. The ratio between the North clock loss and South clock gain is: $$North\ Clock\ :\ South\ Clock$$ $$30:15$$ $$2:1$$ We can use these ratios to find when these clocks show the same time. Since the clocks are 12 hours format, so they will show the same time when: $$North\ clock\ loses=\frac{12}{\left(2+1\right)}\times2=\frac{24}{3}=8hours$$ $$South\ clock\ gains=\frac{12}{\left(2+1\right)}\times1=\frac{12}{3}=4hours$$ Let's find how many hours the North clock loses in a day. North clock loses 30 seconds in one hour. In 24 hours the North clock loses = 30 * 24 = 720 seconds = 12 minutes = 12/60 hours = 0.2 hours The clocks will show the same time after 8/0.2=40 days Therefore, Option C is correct. Hope it helps. I am available if you'd like any follow up. _________________ GMAT Prep From The Economist We offer 70+ point score improvement money back guarantee. Our average student improves 98 points. Free 7-Day Test Prep with Economist GMAT Tutor - Receive free access to the top-rated GMAT prep course including a 1-on-1 strategy session, 2 full-length tests, and 5 ask-a-tutor messages. Get started now. • Free Trial & Practice Exam BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Free Practice Test & Review How would you score if you took the GMAT Available with Beat the GMAT members only code • Free Veritas GMAT Class Experience Lesson 1 Live Free Available with Beat the GMAT members only code • Award-winning private GMAT tutoring Register now and save up to$200

Available with Beat the GMAT members only code

• 5-Day Free Trial
5-day free, full-access trial TTP Quant

Available with Beat the GMAT members only code

• Magoosh
Study with Magoosh GMAT prep

Available with Beat the GMAT members only code

• FREE GMAT Exam
Know how you'd score today for \$0

Available with Beat the GMAT members only code

• Get 300+ Practice Questions

Available with Beat the GMAT members only code

• 5 Day FREE Trial
Study Smarter, Not Harder

Available with Beat the GMAT members only code

### Top First Responders*

1 Ian Stewart 44 first replies
2 Jay@ManhattanReview 35 first replies
3 Brent@GMATPrepNow 34 first replies
4 Scott@TargetTestPrep 31 first replies
5 GMATGuruNY 18 first replies
* Only counts replies to topics started in last 30 days
See More Top Beat The GMAT Members

### Most Active Experts

1 Scott@TargetTestPrep

Target Test Prep

129 posts
2 Max@Math Revolution

Math Revolution

89 posts
3 Ian Stewart

GMATiX Teacher

53 posts
4 Brent@GMATPrepNow

GMAT Prep Now Teacher

50 posts
5 Jay@ManhattanReview

Manhattan Review

35 posts
See More Top Beat The GMAT Experts