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
 7th grade math  Each of the first 4 pit stops a racecar driver makes loses ten ...
 PreCalc  A ferris wheel is 63 feet tall when it reaches its highest point at 8...
 English  1. Cut out all the pieces. (Does 'out' mean 'completely' here?) 2. ...
 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/...
 Math  4 members of a relay team each ran one lap of a race. THeir times were 58...
 math  a red light winks every 6 seconds, a white one every 10 seconds, and a ...
 Calculus (Derivatives)  Two particles are moving in straight lines. The ...
 math  three fireworks are fired at the same time. The first one is fired every ...
More Related Questions