Question

What is ∑n=18(3n−1) equal to? The top number is 8 bottom is n=1

Answer 1

$\bf \sum\limits_{n=1}^{8}~3n-1\implies \sum\limits_{n=1}^{8}~3n-\sum\limits_{n=1}^{8}~1\implies 3\sum\limits_{n=1}^{8}~n-\sum\limits_{n=1}^{8}~1 \\\\\\ 3\left[ \cfrac{8(8+1)}{2} \right]~~-~~(8\cdot 1)\implies 3(36)~~-~~8\implies 108~-~8\implies 100$