Đáp án:

 $A=\dfrac{3}{11}\\
B=\dfrac{1}{5}\\
C=\dfrac{-98}{99}$

Giải thích các bước giải:

 $A=\dfrac{\dfrac{3}{4}-\dfrac{3}{5}+\dfrac{3}{7}+\dfrac{3}{13}}{\dfrac{11}{4}-\dfrac{11}{5}+\dfrac{11}{7}+\dfrac{11}{13}}\\
=\dfrac{3.\left (\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{7}+\dfrac{1}{13}  \right )}{11.\left (\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{7}+\dfrac{1}{13}  \right )}\\
=\dfrac{3}{11}\\
B=\left [\left (\dfrac{2}{193}-\dfrac{3}{386}   \right ).\dfrac{193}{17}+\dfrac{33}{34} \right ]:\left [ \left ( \dfrac{7}{2001}+\dfrac{11}{4002} \right ).\dfrac{2001}{25} +\dfrac{9}{2}\right ]\\
=\left [\dfrac{2}{193}.\dfrac{193}{17}-\dfrac{3}{386}.\dfrac{193}{17}+\dfrac{33}{34} \right ]:\left [  \dfrac{7}{2001}.\dfrac{2001}{25}+\dfrac{11}{4002}.\dfrac{2001}{25} +\dfrac{9}{2}\right ]\\
=\left [\dfrac{2}{17}-\dfrac{3}{2.17}+\dfrac{33}{34} \right ]:\left [  \dfrac{7}{25}+\dfrac{11}{2.25} +\dfrac{9}{2}\right ]\\
=\left [\dfrac{2}{17}-\dfrac{3}{34}+\dfrac{33}{34} \right ]:\left [  \dfrac{7}{25}+\dfrac{11}{50} +\dfrac{9}{2}\right ]\\
=\left [\dfrac{2}{17}+\dfrac{30}{34} \right ]:\left [  \dfrac{14}{50}+\dfrac{11}{50}+\dfrac{225}{50} \right ]\\
=\left [\dfrac{2}{17}+\dfrac{15}{17} \right ]: \dfrac{250}{50}\\
=\dfrac{17}{17}:5\\
=\dfrac{1}{5}\\
C=-\dfrac{1}{99.98}-\dfrac{1}{98.97}-\dfrac{1}{97.96}-...-\dfrac{1}{3.2}-\dfrac{1}{2}\\
=-\left ( \dfrac{1}{99.98}+\dfrac{1}{98.97}+\dfrac{1}{97.96}+...+\dfrac{1}{3.2}+\dfrac{1}{2} \right )\\
=-\left ( \dfrac{1}{98}-\dfrac{1}{99}+\dfrac{1}{97}-\dfrac{1}{98}+\dfrac{1}{96}-\dfrac{1}{97}+...+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{2} \right )\\
=-\left ( \dfrac{-1}{99}+1 \right )\\
=\dfrac{1}{99}-1\\
=\dfrac{1}{99}-\dfrac{99}{99}\\
=\dfrac{-98}{99}$