Question

there are five bells which ring at interval of 4,5,12 and 15 minutes respectively at what minute those bells ring at the same time?​

Answer 1

Answer:   60 minutes

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Explanation:

Let's find the LCM of 4 and 5, which are the first two items of the list.

• multiples of 4 are: 4,8,12,16,20,24,...
• multiples of 5 are: 5,10,15,20,25,...

The smallest item in each list is 20, so the LCM of 4 and 5 is 20.

We can replace the "4,5" in the list "4,5,12,15" with "20". So our new list would be "20,12,15".

We then repeat the process of finding the LCM of the first two items

• multiples of 20 are: 20,40,60,80,...
• multiples of 12 are: 12,24,36,48,60,72,...

LCM of 20 and 12 is 60.

The list "20,12,15" condenses to "60,15".

Repeat this process of finding the LCM once more and you'll find the overall LCM is 60.

Therefore, the LCM of the entire set {4,5,12,15} is 60. This is the smallest multiple shared by all four values. Interestingly enough, the outer values pair up to multiply to 60, and so do the inner values.

4*15 = 60

5*12 = 60

The bells ring together every 60 minutes

In other words, all of the bells ring together at the same time every hour (perhaps at the top of every hour; eg at 7:00 pm and at 8:00 pm, etc).