One lighthouse flashes every 10 seconds, a second lighthouse flashes every 8 seconds. if they flash at the same time, how long will it take to flash at the same time again? a

For this, we need to find the lowest common multiple of 10 and 8

multiples of 10 : 10,20,30,40,50

multiples of 8 : 8,16,24,32,40

so the LCM of 10 and 8 is 40

therefore, they will both flash at the same time again in 40 seconds.