A = $\frac{1}{2}$ + $\frac{5}{99}$ + $\frac{1}{3}$ + $\frac{5}{-99}$
A = ($\frac{1}{2}$ + $\frac{1}{3}$) + ($\frac{5}{99}$ + $\frac{5}{-99}$)
A = ($\frac{3}{6}$ + $\frac{2}{5}$) + ($\frac{5}{99}$ + $\frac{-5}{99}$)
A= $\frac{5}{6}$ + 0
A = $\frac{5}{6}$
Vì $\frac{5}{6}$ < $\frac{7}{6}$ . Vậy ⇒ A < $\frac{7}{6}$