SEAMO 2027 - Paper E - SET 04 - Self-study Question 18

Let $(a_n)$ and $(b_n)$ be arithmetic sequences with $a_1=2019$ and $b_1=1$. Suppose $a_{100}+b_{100}=1010$. Evaluate $a_1+a_2+\cdots+a_{20}+b_1+b_2+\cdots+b_{20}$.

Enter the number only (an exact fraction is allowed).