Correct Answer - Option 1 : 300

Calculation -

The bells will ring together after those time intervals which are common multiples of 5, 15, 20, 25 and 30

So, we have to find the LCM of 5, 15, 20, 25 and 30.

⇒ LCM of 5, 15, 20, 25 and 30 = 2 × 2 × 3 × 5 × 5

⇒ 300

∴ The bells will ring together after 300 seconds.