Five bells ring at an interval of 3 sec, 6 sec, 9 sec, 12 sec and 15 sec respectively. How many times they will ring together in 36 min ?

11 12 13 10

12

LCM of 3, 6, 9, 12 and 15 = 180 It means all the bells will ring together after every 180 sec In 36 min they will ring = \(\frac{36 × 60}{180}\) = 12 times