Four bells ringing together and ring at an interval of 12 sec, 15 sec, 20 sec, and 30 sec respectively. How many times will they ring together in 8 hours?

Question: Four bells ringing together and ring at an interval of 12 sec, 15 sec, 20 sec, and 30 sec respectively. How many times will they ring together in 8 hours?Solution:Four bells ringing timing is 12 sec, 15 sec, 20 sec,30 sec Now we have to take LCM of time interval ⇒ LCM of (12, 15, 20, 30) = 60 Total seconds in 8 hours = 8 × 3600 = 28800 Number of times bell rings = 28800/60 ⇒ Number of times bell rings = 480 If four bells ring together in starting ⇒ 480 + 1 ∴ The bell ringing 481 times in 8 hours.Mistake Points: The bells start tolling together, the first toll also needs to be counted, that is the number of times of tolling since the first time.