Question

one traffic light changes to red every 120 seconds. another traffic light changes to red every 144 seconds. both change to red at 10 00. find the time at which they next change to red together​

Answer 1

120 = 2 × 2 × 2 × 3 × 5

144 = 2 × 2 × 2 × 2 × 3 × 3

LCM of 120 and 144 =

2 × 2 × 2 × 2 × 3 × 3 × 5 = 720

720 seconds = 12 minutes

Both traffic lights will next change to red together at 10:12.