At a traffic signal, a red light flashes two times per minute and a green light flashes six times in five minutes at regular intervals. If both the lights start flashing at the same time, how many times do they flash together in each hour?

Correct option is D

Given:

Red light flashes 2 times per minute.

Green light flashes 6 times in 5 minutes.

Both lights start flashing at the same time.

Solution:

Interval of red light =$$\frac 12$$​ minute.

Interval of green light = $$\frac 56$$​ minute.

LCM of (1, 5) = 5.

HCF of (2, 6) = 2.

Thus, the LCM of $$\frac 12$$​ and $$\frac56 = \frac52.$$​​

In 60 minutes, flashes together = $$\frac{60}{\frac52 }=\frac{ 120}5$$​ = 24 flashes.