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Aptitude - Problems on H.C.F and L.C.M - Discussion

Discussion Forum : Problems on H.C.F and L.C.M - General Questions (Q.No. 3)
Problems on H.C.F and L.C.M
3.
Six bells commence tolling together and toll at intervals of 2, 4, 6, 8 10 and 12 seconds respectively. In 30 minutes, how many times do they toll together ?
4
10
15
16
Answer: Option
Explanation:

L.C.M. of 2, 4, 6, 8, 10, 12 is 120.

So, the bells will toll together after every 120 seconds(2 minutes).

In 30 minutes, they will toll together 30 + 1 = 16 times.
2

Discussion:
171 comments Page 8 of 18.
Prem said:   1 decade ago
I am unable to understand why we are using lcm method for this problem. Can anyone explain?
Atishay said:   1 decade ago
Why not using HCM:

Suppose 3 bells are tolling at 2, 4, 6 sec,

HCM is 2, so now think, is it possible that they will toll at every 2 sec. NO.

We will have to find a common number (multiple) which is occurring to every bell and that is called LCM.

So LCM here is 12.

That means every bell will toll at 12th second.
Rohan bhoir said:   1 decade ago
Can you tel me how is the HCM can find? Explain with any example.
Pri said:   1 decade ago
Please explain me HCM. I can't get clear idea about it.
Upendra said:   1 decade ago
Why 1 added?
Saikiran said:   1 decade ago
Six bells commence tolling together means six bells started tolling together that's why 1 is added to 15, now 15+1=16.

Commence=Start or begin.
Sumit chauhan said:   1 decade ago
But why are we add 1? Because when we toll together all the ball. They toll together. And that time also count in first 30 min.
Divi said:   1 decade ago
Very clear explanation. Thank you.
Shrinivasmutagar said:   1 decade ago
Why that 120 sec have been took?
Mahesh said:   1 decade ago
How do you get that 120?
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