Question

Lighthouse A sounds a foghorn every 4 hours, and Lighthouse B sounds a foghorn every 10 hours.

If both lighthouses sound their foghorns at the same time, how many hours will it be until the next instance when both foghorns sound at the same time?

14 hours

20 hours

24 hours

40 hours

Answer 1

20 hours

Explanation:

Answer 2

The answer will be 20.

Explanation:

If both lighthouses A and B sound their foghorns at the same time, it will be after 20 hours before both foghorns sound at the same time again.

Since lighthouse A sounds it's foghorn every 4 hours, and lighthouse B sounds it's foghorn every 10 hours.

To determine the next time when both foghorns sound at the same time;

We need then need to determine the lowest common multiple (LCM) of 4 and 10.

The lowest common multiple of 4 and 10 is going to be 20.

Therefore they will sound at the same time after 20 hours.