Đáp án:
Giải thích các bước giải:
$B=2.5+5.8+...+101.104$
$3:B=3:(2.5+5.8+...+101.104)$
$\dfrac{3}{B}=\dfrac{3}{2.5}+\dfrac{3}{5.8}+...+\dfrac{3}{101.104}$
$\dfrac{3}{B}=\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+\dfrac{1}{8}-...+\dfrac{1}{101}-\dfrac{1}{104}$
$\dfrac{3}{B}=\dfrac{1}{2}-\dfrac{1}{104}$
$\dfrac{3}{B}=\dfrac{51}{104}$
$B=3:\dfrac{51}{104}$
$B=\dfrac{312}{51}=\dfrac{104}{17}$
