Lời giải:
$A=\dfrac{1}{2.5}+\dfrac{1}{5.8}+\dfrac{1}{8.11}+...+\dfrac{1}{95.98}$
$3A=(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{11}+...+\dfrac{1}{95}-\dfrac{1}{98})$
$3A=(\dfrac{1}{2}-\dfrac{1}{98})$
$3A=\dfrac{24}{49}$
$A=\dfrac{24}{49}÷3$
$A=\dfrac{8}{49}$