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HKIMO 2026 Grade 8 National Preliminary Set 05 Question 13

HKIMO · HKIMO 2026 Grade 8 National Preliminary Set 05

Question 13

Find the units digit of $A=1+7+7^2+7^3+\cdots+7^{99}+7^{100}$.
  1. 1
  2. 3
  3. 7
  4. 9