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At a telephone exchange, three phones ring at intervals of 20 sec, 24 sec and 30 seconds - If they ring together at 11:25 am, when will they next ring together?1). 11:29 pm2). 11:27 am3). 11:51 am4). 12:29 pm

Answer»

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 = 120/60 = 2 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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