($\frac{5}{101.99}$ + $\frac{5}{99.97}$ + $\frac{5}{97.95}$ +...+ $\frac{5}{5.3}$ + $\frac{5}{3.1}$) - x = 3
⇔ ($\frac{5}{1.3}$ + $\frac{5}{3.5}$ + ...+ $\frac{5}{95.97}$ + $\frac{5}{97.99}$ + $\frac{5}{99.101}$) - x = 3
⇔ $\frac{5}{2}$($\frac{2}{1.3}$ + $\frac{2}{3.5}$ + ...+ $\frac{2}{95.97}$ + $\frac{2}{97.99}$ + $\frac{2}{99.101}$) - x = 3
⇔ $\frac{5}{2}$(1 - $\frac{1}{3}$ + $\frac{1}{3}$ - $\frac{1}{5}$ +...+ $\frac{1}{97}$ - $\frac{1}{99}$ + $\frac{1}{99}$ - $\frac{1}{101}$) - x = 3
⇔ $\frac{5}{2}$(1 - $\frac{1}{101}$) - x = 3
⇔ $\frac{5}{2}$ . $\frac{100}{101}$ - x = 3
⇔ $\frac{250}{101}$ - x = 3
⇒ x = $\frac{250}{101}$ - 3
⇒ x = $\frac{250}{101}$ - $\frac{303}{101}$
⇒ x = -$\frac{53}{101}$
Vậy không có đáp án đúng.
---------------------------------
Xin hay nhất ạ!!~
