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SEAMO 2026 Paper A SET 1 – Self-practice Question 9

SEAMO · SEAMO 2026 Paper A SET 1 – Self-practice

Question 9

Find the value of $1-2+3-4+5-6+\cdots-20+21$.
  1. 11
  2. 13
  3. 15
  4. 17
  5. 21