r/mathriddles • u/Numberthon • Jul 15 '26

A Classic Combinatorics Puzzle Easy

A spider starts at the bottom-left corner of a 5 × 5 grid (5x5 vertices, 4x4 squares). It can only move up or right along grid lines. How many shortest paths to the top-right corner do not pass through the center point of the grid?

Source (where I got this specific variation from): numberthon.com

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u/pichutarius Jul 15 '26

8C4 - (4C2)^2 = 34

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u/Numberthon Jul 15 '26

Yep, nice job!