The Last Ball

A bag has 20 blue and 14 red balls. You repeatedly remove 2 balls: if same color, add a blue ball; if different, add a red ball. What color is the last remaining ball?

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Quick Answer & Explanation

Red. Each step reduces

The answer to this riddle is Red. Each step reduces. Difficulty: Hard · Solved by 21,757 puzzle lovers.

Red. Each step reduces the count by 1. Red balls decrease by 0 or 2 each step (always staying odd). Since we started with 14 (even) red balls... Actually: the parity of red balls is preserved (14 = even). But we always end with 1 ball. An even operation ending at 1 means the last ball is blue. Wait: 14 is even. If 2 reds removed, reds decrease by 2 (stays even). If different, reds stay same... Actually the last ball is blue.

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