Two fire sirens give alarms at intervals of 5/7, 7/8 hours. Since these two fire sirens sounded an alarm at 04:00 on Friday at the same time, on which day and at what time do they alarm together again?
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To determine when the two alarms will sound together again, we need to find the lest common multiple between the two intervals.
LCM
LCM(5,7) is given by
HCF(7,8) = 1
Therefore, LCM = 35
This means that the two sirens will alarm together again after 35 hours. Since they both sounded at 04:00 of Friday, we add 35 hours to this time and get, 15:00 on Saturday.