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)
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 ?
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:
172 comments Page 18 of 18.
Sundar said:
2 decades ago
If two bells toll after every 3 secs and 4 secs respectively and if they commence tolling at the same time.
Then the first bell tolls after every 3, 6, 9, 12 secs...
The second bell tolls after every 4, 8, 12, ....
So they toll together again after 12 secs, which is the LCM
Henceforth they toll after every 12 seconds, i.e whenever the time is a common multiple of both 3 and 4.
Since the bells start tolling together, the first toll also needs to be counted. Therefore we need to add 1.
Then the first bell tolls after every 3, 6, 9, 12 secs...
The second bell tolls after every 4, 8, 12, ....
So they toll together again after 12 secs, which is the LCM
Henceforth they toll after every 12 seconds, i.e whenever the time is a common multiple of both 3 and 4.
Since the bells start tolling together, the first toll also needs to be counted. Therefore we need to add 1.
(2)
Punk said:
2 decades ago
Why 1 is added? please explain.
Post your comments here:
Quick links
Quantitative Aptitude
Verbal (English)
Reasoning
Programming
Interview
Placement Papers