A red light flashes 3 times per minute and a green light flashes 5 times in 2 minutes at regular intervals. If both lights start flashing at the same time, how many times do they flash together in each hour?

1) 30
2) 24
3) 20
4) 60

• 1) 30
  Red light flashes 3 times/min.=Once in 20 sec.
  Green light flashes 5 times/2 min.=Once in 24 sec.
  Instance they flashes together=their L.C.M =120 sec.=Once in 2 minutes
  So in One Hour both flashes together=60/2=30 times
  
• 11 years agoHelpfull: Yes(2) No(0)