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HKIMO 2026 Grade 6 National Preliminary Set 05 Question 8

HKIMO · HKIMO 2026 Grade 6 National Preliminary Set 05

Question 8

Find $1\times 2+2\times 3+3\times 4+\cdots+20\times 21$.
  1. 2680
  2. 2880
  3. 2780
  4. 3080