This question was previously asked in

Delhi Forest Guard Previous Paper 1 (Held on: 3 March 2021 Shift 3)

Option 2 : 7

ST 1: Logical reasoning

5280

20 Questions
20 Marks
20 Mins

**Calculation:**

LCM of (20, 25, 30 and 40) = 2 × 2 × 5 × 5 × 3 × 2 = 600 seconds

so, after every 600 seconds all 4 bells toll together

1 hours = 60 minutes

In 1 hours = 3600 seconds

So, no. of time they toll together in hour = (3600/600) + 1 = 7 times

**∴ They toll together in an hour is 7 times**

__Mistake Points__

In these type of question we assume that we have started counting the time after first ringing. Due to this when we calculate the LCM it gives us the ringing at 2nd time not the first time. So, we needed to add 1