Answer: 30% (choice B)
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Step-by-step explanation:
Consider a square with side length 1 unit.
Draw a diagonal and we have two congruent isosceles right triangles. Each triangle has a hypotenuse of sqrt(2) after using the pythagorean theorem.
If the person walks along the edges, then they walk 1+1 = 2 units.
If they walk along the diagonal, they walk roughly sqrt(2) = 1.4142 units.
They save roughly 2-1.4142 = 0.5858 units
which is roughly 0.5858/2 = 0.2929 = 29.29% of the walked distance along the edges. There's probably some slight rounding error going on, but it's fairly close to 30%, so that is likely the final answer.