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HKIMO 2026 Grade 4 National Preliminary Set 05 Question 13

HKIMO · HKIMO 2026 Grade 4 National Preliminary Set 05

Question 13

Define $a\oplus b=(a-b)\times(a+b)$. Find $89\oplus19$.
  1. 7560
  2. 108
  3. 1691
  4. 8640