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Ben and Peter start off together on a 18 km hike.
Ben walks 3 times as fast as Peter, and when he comes to the end of the hike
he turns around and walks back to meet Peter.
How far, in km, has Peter walked when they meet?
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This problem is a kind that even a smart kindergarten child can guess the answer.
The full distance of 18 km consists of two halves of 9 km eacn.
When Peter (the slower person) will cover one half,
Ben (the faster person) will cover 3 halves.
In other words, when Peter (the slower person) will cover half of the distance
moving forward, Ben (the faster person) will cover the entire distance (two halves)
and the third half returning back.
So, their meeting point is the midpoint between the endpoints remoted at 18 km.
Peter will walk 9 kilometers. ANSWER
Solved.