Đáp án:

$\text{A < 5}$

Giải thích các bước giải:

$\text{A = $\dfrac{10}{1.3}$ + $\dfrac{10}{3.5}$ + $\dfrac{10}{5.7}$ + ... + $\dfrac{10}{33.35}$}$

$\text{A = $\dfrac{5.2}{1.3}$ + $\dfrac{5.2}{3.5}$ + $\dfrac{5.2}{5.7}$ + ... + $\dfrac{5.7}{33.35}$}$

$\text{A = 5 . ( $\dfrac{2}{1.3}$ + $\dfrac{2}{3.5}$ + $\dfrac{2}{5.7}$ + ... + $\dfrac{2}{33.35}$}$

$\text{A = 5 . ( $\dfrac{1}{1}$ - $\dfrac{1}{3}$ + $\dfrac{1}{3}$ - $\dfrac{1}{5}$ + $\dfrac{1}{5}$ - $\dfrac{1}{7}$ + ... + $\dfrac{1}{33}$ - $\dfrac{1}{35}$ )}$

$\text{A = 5 . ( $\dfrac{1}{1}$ - $\dfrac{1}{35}$ )}$

$\text{A = 5 . $\dfrac{34}{35}$}$

$\text{ Vì $\dfrac{34}{35}$ < 1}$

$\text{⇒ 5 . $\dfrac{34}{35}$ < 5 }$

$\text{⇒ A < 5}$

$\text{Vậy A < 5}$