Enigmatic Code

Programming Enigma Puzzles

Puzzle #50: Crossing the river

From New Scientist #3273, 14th March 2020 [link] [link]

Petal is on her way to a country fair, to sell some vintage kitchenware belonging to her good friend Gretel. As she walks along the River Biddle admiring the view, Petal trips on a pair of oars left carelessly on the bank. A valuable wrought-iron kettle flies out of her hand and lands on one of the river’s many marshy islands.

From the river bank to the island is 3 metres directly across, and though the oars are sturdy enough to walk on, they are just short of reaching over the water.

How can Petal reach reach the island with the paddles and save Gretel’s metal kettle from its muddy peril?


One response to “Puzzle #50: Crossing the river

  1. Jim Randell 14 March 2020 at 1:19 pm

    You could use one of the oars to turn part of curved bank into a straight line, which will be slightly closer to the island than the bank itself. The second oar can then be used to bridge from the first oar to the island.

    If x is the length of the oar, this situation is possible if:

    sqrt(6² – (x/2)²) – 3 < x
    ⇒ x > (6/5)(sqrt(19) – 2)

    Roughly: 2.831 < x < 3.

    Or maybe it would be better to use the oars as stilts and walk across.

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