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AIMO 2021 Senior secondary — Preliminary (Open Trial 1) Question 3

AIMO · AIMO 2021 Senior secondary — Preliminary (Open Trial 1)

Question 3

With $\sum_{i=a}^{b}f(i)=f(a)+f(a+1)+\cdots+f(b)$, evaluate $\sum_{i=1}^{10}\frac1{(2i-1)(2i+1)}$.
  1. $1/3$
  2. $9/21$
  3. $10/21$
  4. $4/5$