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Math Riddle!!!

So I'm taking this "math in society" class as my very last required credit so I can graduate this spring (YAY) and we do these riddle type problem solving questions. I'll admit, I'm totally not getting this one so I"m wondering if someone can help me out! I don't want just the answer, I'm looking for an explanation so I know what to look for, so I know how to figure this out. they aren't for credit, theyre just excercises, so I'm not trying to pull a fast one on my teacher lol.



Shrek and Donkee are on an adventure. They are searching for a comb made of rubies. Eventually they reach a lake that is shaped like a square. In the middle of the lake is an island and on the island is the ruby comb. Using a rope with feet markings on it, Shrek and Donkee discover that it is 20 feet from the edge of the lake to the island. (See the figure below.) If there are two wooden planks that are 18 feet long how will Shrek and Donkee retrieve the ruby comb? There is no way to attach the two boards together to make one long board

 You can't assume they can swim and they can't walk on the boards because you can't assume the boards will float.


Asked by ElsaSalsaaa at 7:24 PM on Apr. 5, 2011 in Just for Fun

Level 20 (9,139 Credits)
This question is closed.
Answers (4)
  • So to figure where to put the first board use Pythagorean Theorem and say 2x squared = c squared. Board would go equally down two sides from one corner. So, figure one foot over each side to support board and that leaves 16 feet to work with. So, 2x squared = 16 squared; x squared = 128; x = 11.3137085. The board gets put 11.3137085 feet down, from one corner, on each side to make first triangle. The second board gets put from the middle of the first board to the island.

    Answer by elizabr at 8:14 PM on Apr. 5, 2011

  • Use the 18 foot board to walk within 2 feet of the island then use the rope to lasoo the comb???

    Answer by vbruno at 7:29 PM on Apr. 5, 2011

  • My DH says put one board from one side to the other side making a triangle out of one corner. Then put the second board going from the middle of that first board over to the island. Walk on the board to get to the comb. Hope I explained it good enough.

    Answer by elizabr at 7:35 PM on Apr. 5, 2011

  • I am an engineer and I would do the same thing as elizabr's DH suggested.
    However I can't figure it out mathematically. If it was 20 feet from the edge of the lake to the middle of the Island, you could easily use pythagorus and trig to figure out where you need to put the first plank in order for the second one to reach the island. The way it is though? I think you're going to need calculus.

    Answer by onethentwins at 7:54 PM on Apr. 5, 2011