
Elementary Math Fractions, Percentages, Word Problems, Equations, Inequations, Factorization, Expansion 
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May 1st, 2019, 11:26 PM  #1 
Senior Member Joined: Aug 2014 From: India Posts: 458 Thanks: 1  How to solve this fast and slow clock problem?
At 3:00 pm, clock was showing regular time. There are two clocks, one gains 5 min per hour. Another one loses 5 mins per hour. After how many hours both clocks will show the same time again?

May 2nd, 2019, 04:45 AM  #2 
Global Moderator Joined: Dec 2006 Posts: 20,926 Thanks: 2205 
Do the two clocks show whether the time is am or pm?

May 3rd, 2019, 03:10 AM  #3 
Senior Member Joined: Aug 2014 From: India Posts: 458 Thanks: 1  
May 3rd, 2019, 05:45 AM  #4 
Global Moderator Joined: Dec 2006 Posts: 20,926 Thanks: 2205 
If the clocks show the same time initially, they'll next do that when they're out of step with each other by 24 hours (because they don't show the date). They get out of step with each other by 10 minutes every hour, so this will take 144 hours (because 1440 minutes is 24 hours).

May 8th, 2019, 08:10 AM  #5  
Senior Member Joined: Aug 2014 From: India Posts: 458 Thanks: 1  Quote:
 
May 8th, 2019, 06:06 PM  #6 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 14,597 Thanks: 1038  
May 8th, 2019, 11:07 PM  #7 
Senior Member Joined: Aug 2014 From: India Posts: 458 Thanks: 1 
Each hour clock A runs 5 minutes fast, after 12 hours, clock A is indicating 1 hour later than it should be. Although it is 3, it shows 4. Similarly, because each hour clock B runs 5 minutes slow, after 12 hours, clock B is indicating 1 hour earlier than it should be. Although it is 3, it shows 2. At t = 0h: Clock A points to 3. Clock B points to 3. At t = 12h: Clock A points to 4. Clock B points to 2. At t = 24h: Clock A points to 5. Clock B points to 1. At t = 36h: Clock A points to 6. Clock B points to 12. At t = 48h: Clock A points to 7. Clock B points to 11. At t = 60h: Clock A points to 8. Clock B points to 10. At t = 72h: Clock A points to 9. Clock B points to 9. 
May 9th, 2019, 05:48 AM  #8 
Global Moderator Joined: Dec 2006 Posts: 20,926 Thanks: 2205 
The times (after 72 hours) wouldn't match, as one would be 9 pm and the other 9 am.


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clock, fast, problem, slow, solve 
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