If both lighthouses A and B sound their foghorns at the same time, it will be after 30 hours before both foghorns sound at the same time again.
To determine the next time when both foghorns sound at the same time;
We need to determine the lowest common multiple (LCM) of 3 and 10.
As such, the foghorns sound at the same time after 30 hours of when the foghorns sounded the same time.
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