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On a merry-go-round that spins counter-clockwise, 9 horses are evenly spaced on the outside perimeter,
numbered clockwise. Abe stands next to horse number 1 and starts counting time as the merry-go-round begins
to turn. He notices that It takes six seconds for horse number 4 to reach him. How long will it take
the merry-go-round to go all the way around once?
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In all, there are 9 equal gaps between the neighbor horses along the circumference,
and there are 3 equal gaps from horse 1 to horse 4.
So, the way from horse 1 to horse 4 is one third of the entire circumference.
Therefore, the time for one full revolution is three times 6 seconds, or 3*6 = 18 seconds. ANSWER
Solved.