Đáp án: $\text { = $\frac{11}{23}$ }$
Giải thích các bước giải:
$\text { $\frac{1}{3}$ + $\frac{1}{15}$ + $\frac{1}{35}$ + ... + $\frac{1}{399}$ + $\frac{1}{483}$ }$
$\text { = $\frac{1}{1.3}$ + $\frac{1}{3.5}$ + $\frac{1}{5.7}$ + ... + $\frac{1}{19.21}$ + $\frac{1}{21.23}$ }$
$\text { = $\frac{1}{2}$ . (1 - $\frac{1}{3}$ + $\frac{1}{3}$ - $\frac{1}{5}$ + $\frac{1}{5}$ - $\frac{1}{7}$ + ... + $\frac{1}{19}$ - $\frac{1}{21}$ + $\frac{1}{21}$ - $\frac{1}{23}$) }$
$\text { = $\frac{1}{2}$ . (1 - $\frac{1}{23}$) }$
$\text { = $\frac{1}{2}$ . $\frac{22}{23}$ }$
$\text { = $\frac{11}{23}$ }$
