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IKMC 2012 - Grades 9-10 - Self-study Question 4

IKMC · IKMC 2012 - Grades 9-10 - Self-study

Question 4

Alice encodes each letter as A=01, B=02, …, Z=26, then sends 2 ×number+9. Bob receives 25−19−45−38. What was the original message?
  1. HERO
  2. HELP
  3. HEAR
  4. HERS
  5. Alice made a mistake