Posted by **DJAZIA** on Friday, February 20, 2009 at 4:06pm.

THERE ARE 3 LIGHT HOUSES,THE FIRST ONE SHINE FOR 3 SECONDS, THEN IS OFF FOR 3 SECONDS.the 2 one shine for 4 seconds then is off for 4 seconds.the 3 one shine for 5 seconds,then is off for 5 seconds.all thr 3 lights have just come together.when is the first time that all the three lights will come off?.when is the next time that all the three lights will come on at the same moment?

- NUKMERACY -
**drwls**, Friday, February 20, 2009 at 5:37pm
The period between the beginning of a "shine" is 6 seconds for #1, 8 seconds for #2 and 10 seconds for #3. the lowest common multiple of those numbers is 2*3*2*2*5 = 120 seconds. That is when they will come ON together for the next time.

When they come OFF together is more complicated. #1 goes off at t = 3, 9, 15, 21, 27, etc s. #2 goes off at 4, 12, 20, 28, 36.. s. One set of number is odd and the other even. The "off" times can never coincide.

Maybe another teacher will prove me wrong about this

## Answer This Question

## Related Questions

- English - 1. Cut out all the pieces. (Does 'out' mean 'completely' here?) 2. ...
- English - 1. This book is really fun. 2. This book is real fun. 3. This book is ...
- 7th grade math - Each of the first 4 pit stops a racecar driver makes loses ten ...
- math - a red light winks every 6 seconds, a white one every 10 seconds, and a ...
- Pre-Calc - A ferris wheel is 63 feet tall when it reaches its highest point at 8...
- Math - 4 members of a relay team each ran one lap of a race. THeir times were 58...
- Physics - A ball is rolled off a horizontal roof at 6m/sec , after leaving the ...
- Physics - If the vertical component of velocity for a projectile is 7.3 meters/...
- Physics - If the vertical component of velocity for a projectile is 7.3 meters/...
- Calculus (Derivatives) - Two particles are moving in straight lines. The ...

More Related Questions