Alight flashes every 2 minutes, a second light flashes every 3.5 minutes and a third light flashes every 4 minutes. if all three lights flash together at 8 p. m what us the next time of the day they will all flash together

Take the LCM of the three numbers. Since 2 is a multiple of 4, you can ignore the two and just take the LCM of 4 and 3.5. Since 3.5 is a decimal, the LCM is just 3.5*4 which is 14. That is how many minutes after 8:00 they will flash together again.