At a telephone exchange, three phones ring at intervals of 20 sec, 24 sec and 30 seconds. If they ring together at 11 : 25 a.m. When will they next ring together?
At a telephone exchange, three phones ring at intervals of 20 sec, 24 sec and 30 seconds. If they ring together at 11 : 25 a.m. When will they next ring together?
A11 : 29 a.m.
B11 : 27 a.m.
C11 : 51 a.m.
D12 : 29 p.m.
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Correct answer is: 11:27 a.m.
Explanation:
Time taken by three phones to ring together = LCM of 20, 24 and 30
⇒ Time taken by three phones to ring together = 120 seconds
(? 1 min = 60 seconds)
⇒ Time taken by three phones to ring together = \(\frac{120}{60} = 2 \text{ min}\)
If the three phones ring together at 11:25 am then they will next ring together after 2 minutes i.e. at 11:27 am.
∴ Time at which the phones next ring together = 11:27 am
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