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2021 Math Kangaroo

Problem 3

Problem 3 · 2021 Math Kangaroo Medium
Spatial & Visual Reasoning path-tracing

A park is shaped like an equilateral triangle. A cat wants to walk along one of the three indicated paths (thicker lines) from the upper corner to the lower-right corner. The lengths of the paths are P, Q and R, as shown. Which statement about the lengths of the paths is true?

Figure for Math Kangaroo 2021 Problem 3
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Answer: B — \(P
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Hint 1 of 2
Every path starts at the top corner and ends at the lower-right corner, so they all cover the same overall drop and shift.
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Hint 2 of 2
Replacing a straight horizontal cut with travel along the slanted edge adds length, so compare how much of each path hugs the slant.
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Approach: compare the three traced paths segment by segment
  1. All three paths join the same two corners, so they share the same net horizontal and vertical change.
  2. Path P takes the most direct mix of horizontal cuts and short drops, so it is the shortest.
  3. Path Q runs the most along the slanted edge, where covering the same height costs extra length, so it is the longest, with R in between.
  4. Therefore \(P(B).
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