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BEBRAS 2025 Grade 9-10 Round 2 Ext Question 13

BEBRAS · BEBRAS 2025 Grade 9-10 Round 2 Ext

Question 13

Alice and Bob’s secret box takes two passwords of equal length, written only with @ and #, and creates a common binary password. At each position it writes 0 if their symbols agree, and 1 if they differ.

Question illustration

If the common password is 0110, which pair could Alice and Bob have entered?
  1. “@ # @ #” and “# @ @ #”
  2. “@ # @ #” and “@ @ # #”
  3. “# @ @ #” and “# @ # @”
  4. “@ @ @ #” and “@ # @ @”