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BEBRAS 2017 Grade 5-6 Round 2 Ext Question 4

BEBRAS · BEBRAS 2017 Grade 5-6 Round 2 Ext

Question 4

Four guests each bring one gift to a party. Each guest gives a gift to another guest, and each guest receives exactly one gift. Nobody gives to themselves. We write Art→Bran when Art gives to Bran; if Art gives to Bran and Cáit gives to Art, we write Art→Bran, Cáit→Art.

Question illustration

Which gift exchange obeys all the rules?
  1. Art→Bran, Cáit→Dara, Dara→Bran, Bran→Art
  2. Cáit→Dara, Dara→Bran, Art→Cáit, Cáit→Art
  3. Dara→Bran, Art→Dara, Cáit→Art, Bran→Cáit
  4. Bran→Cáit, Cáit→Art, Dara→Bran, Art→Cáit