A light flashes every two minutes a second light flashes every 3.5 minutes and a third light flashes every four minutes if all three lights flash together at 8 PM what is the next time of the day they were all flash together

The answer should be 8:28 pm

Multiples of 2: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28

Multiples of 3.5: 3.5, 7, 10.5, 14, 17.5, 21, 24.5, 28

Multiples of 4: 4, 8, 12, 16, 20, 24, 28

The least common multiple of the 3 numbers is 28, so the lights will flash at the same time every 28 minutes.

The time will be 8:28 PM