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A bicycler traveling 12 mph passes a runner traveling 9 mph.
If the runner started at noon, and the bicycler at 12:30, how far from the start point did they meet?
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When the bicycler started at 12:30, the runner was 9*0.5 = 4.5 miles ahead.
The approaching speed was 12-9 = 3 mph, so the bicycler catch up the runner in 4.5/3 = 1.5 hours.
During this time, the bicyclist covered 1.5*12 = 18 miles from the start.
So, the distance from the start to the meeting point was 18 km. ANSWER
Solved.