A farmer builds a rectangular pasture against a straight stone wall. He has 100 meters of fencing to enclose the other three sides. What dimensions will yield the maximum possible area for his animals?
50 meters parallel to the wall, and 25 meters for each of the two perpendicular sides.
Let width be $w$ and length parallel to wall be $l$. Fencing is $2w + l = 100$, so $l = 100 - 2w$. Area $A = w(100 - 2w) = 100w - 2w^2$. Maximizing this quadratic yields $w = 25$ and $l = 50$.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Medium. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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