$A$ = $\frac{1}{1.4}$ + $\frac{1}{4.7}$ +......+ $\frac{1}{94.97}$
= $\frac{1}{3}$ . ( $\frac{3}{1.4}$ + $\frac{3}{4.7}$ +......+ $\frac{3}{94.97}$ )
= $\frac{1}{3}$ . ( $1$ - $\frac{1}{4}$ + $\frac{1}{4}$ - $\frac{1}{7}$ +......+ $\frac{1}{94}$ - $\frac{1}{97}$)
= $\frac{1}{3}$ . ( $1$ - $\frac{1}{97}$)
= $\frac{1}{3}$ . $\frac{96}{97}$
= $\frac{32}{97}$
$Vậy$ $A$ = $\frac{32}{97}$
