SEAMO X 2019 — Paper C — Grade 5–6 Question 5

A special operation is defined by $5\times2=5+6=11$, $3\times4=3+4+5+6=18$, $6\times3=6+7+8=21$. Evaluate $1\times9+2\times9+\cdots+9\times9$ using this operation.