Lời giải:
Đặt biểu thức là A:
$A=\dfrac{\dfrac{1}{3}-\dfrac{1}{7}-\dfrac{1}{13}}{\dfrac{2}{3}-\dfrac{2}{7}-\dfrac{2}{13}}×\dfrac{\dfrac{1}{3}-0,25+0,2}{1\dfrac{1}{6}-0,875+0,7}$
$A=\dfrac{\dfrac{1}{3}-\dfrac{1}{7}-\dfrac{1}{13}}{2(\dfrac{2}{3}-\dfrac{2}{7}-\dfrac{2}{13})}×\dfrac{\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{5}}{\dfrac{7}{6}-\dfrac{7}{8}+\dfrac{7}{10}}$
$A=\dfrac{1}{2}×\dfrac{\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{5}}{\dfrac{7}{6}-\dfrac{7}{8}+\dfrac{7}{10}}$
$A=\dfrac{1}{2}×\dfrac{\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{5}}{\dfrac{7}{2}\bigg(\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{5}\bigg)}$
$A=\dfrac{1}{2}×\bigg(\dfrac{\dfrac{1}{7}}{2}\bigg)$
$A=\dfrac{1}{2}×\dfrac{2}{7}$
$A=\dfrac{1}{7}$
