$A=$$\frac{4}{5.7}$ + $\frac{4}{7.9}$ +...+ $\frac{4}{53.55}$
⇔$A=$$2$.($\frac{2}{5.7}$ + $\frac{2}{7.9}$ +...+ $\frac{2}{53.55}$)
⇔$A=$$2$.($\frac{1}{5}$ - $\frac{1}{7}$ +$\frac{1}{7}$ - $\frac{1}{9}$ +...+$\frac{1}{53}$ - $\frac{1}{55}$ )
⇔$A=$$2$.($\frac{1}{5}$ - $\frac{1}{55}$)
⇔$A=$$2$.$\frac{10}{55}$
⇔$A=$$\frac{20}{55}$
⇔$A=$$\frac{4}{11}$
