Question

Four gongs strike at intervals of 30 60 90 and 150 respectively. At what time will they strike together again next, if they start simultaneously at 12 noon .

Answer 1

they will strike again in 300 sec( lcm )
300 sec=5 mins
therefore they will strike at 12:05

Answer 2

the question is nothing but to find the LCM of the intervals.
30 = 2*5*3
60 = 2^2*3*5
90 = 2*5*3^2
150 = 2*5^2*3
so LCM = 2^2 * 3^2 *5^2 = 4 * 9 * 25 = 900
so the gongs will ring after 900 units time
here it is not given if it is seconds or minutes or hours
so time can't be specified