mersenneforum.org Rendezvouz With A Log
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 2003-11-10, 15:35 #1 koal   Nov 2002 Vienna, Austria 518 Posts Rendezvouz With A Log Hi There! Imagine a trapper canoeing upstream on the Yukon river. He starts at a small village and after one mile he has a kind of collision with a huge log. The collision does neither hurt him nor his canoe, but at that point he loses his bottle of whiskey. The bottle is twice as big as it has to be (thus the bottle is either half full or half empty). 10 minutes after the collision the man recognizes the loss of the bottle. He immediately turns his boat, and – rowing at the same speed relatively to the river, as he did upstream - he reaches his bottle exaclty at the village, where hie started. Now what’s the river Yukon’s speed at that region? Usual handling with collisions and direction changes => they cost NO time.
 2003-11-16, 17:27 #2 Jahodas   Nov 2003 K-Vegas 2 Posts A bit of algebra gave me 20xy=x [where y is the speed of the river in miles per minute and x is the speed the guy is paddling]. So y=1/20 mpm = 3 mph? I'm new here, btw.
 2003-11-17, 02:05 #3 koal   Nov 2002 Vienna, Austria 518 Posts Maybe we can talk about your solution a few days later in detail. Once we agreed, not to post results here directly, no matter, if they're are true or false, but via private message ...
 2003-11-17, 05:05 #4 Wacky     Jun 2003 The Texas Hill Country 2×541 Posts I wouldn't be too hard on Jahodas. After all, he is new. Besides, the puzzle has been posted for almost a week with no evidence of activity. I suggest that is more than enough time for anyone interested in solving the puzzle to have either sent you a private message or made public inquiries.
 2003-11-28, 12:40 #5 koal   Nov 2002 Vienna, Austria 41 Posts The solution: The bottle has no speed relatively to the river, i.e. it travels with the Yukon river’s speed. From the bottle’s point of view, itself does not move compared to the water, the trapper is canoeing away for 10 minutes, then coming back at the same speed relatively to the water, reaching the bottle after a total of 20 minutes. Within that time the whole thing (i.e. the Yukon river with a bottle and a canoeing trapper on it) has moved 1 Mile, so the bottle is at the village, where the trapper started, which results in a speed of 3 miles per hour for the Yukon river.