Question

The traffic lights at three different road crossing change after every 48 secs, 72 secs and 108 secs respectively. If they change simulatenously at 7 a.m. at what time will they change simulatenouslyagain

Answer 1

48 = 2 * 2 * 2 * 2 * 3
72 = 2 * 2 * 2 * 3 * 3 
108 = 2 * 2 * 3 * 3 * 3
LCM (48; 72; 108) = 432

432 secs = 7,2 min. = 7 min.12 secs

7 a.m. + 7 min.12 secs = 7:07:12 a.m. - answer.