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The traffic lights at 3 different road crossings change after every 48sec., 72sec., 108sec. respectively.If they change simultaneously at 7a.m., at what time will they change simultaneously again?
 Interval of change = (L.C.M of 48,72,108)sec.=432sec.
       So, the lights will agin change simultaneously after every 432 seconds i.e,7 min.12sec
       Hence , next simultaneous change will take place at 7 + 7min.12sec
                                            =7:7:12 a.m


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