Question

three bells ring simultaneously at 11pm .they rang at regular intervals of 15 mins ,20 mins,30 mins ,.at what time the all three bells ring together​

Answer 1

LCM of 15 20 and 30 minutes = 60 minutes = 1 hr

So they will ring together after every 1 hour.

As they ring together at 11 a.m. so they will again ring after 1 hour .

That is 11+1=12 PM.