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SMO 2005 Junior Round 1 Question 3

SMO · SMO 2005 Junior Round 1

Question 3

What is the last two digits of $1+2+3+4+\cdots+2003+2004+2005$?
  1. $00$
  2. $15$
  3. $25$
  4. $50$
  5. $75$