Đáp án:

 $A=\dfrac{953}{32}\\
B=\dfrac{1708}{57}\\
2)
a)\dfrac{8}{3}\\
b)\dfrac{-1}{6}\\
c)\dfrac{15}{28}\\
3)
a)\dfrac{-52}{135}\\
b)5$

Giải thích các bước giải:

 $A=49\dfrac{8}{23}-\left (5\dfrac{7}{32}+14\dfrac{8}{23}  \right )\\
=49\dfrac{8}{23}-5\dfrac{7}{32}-14\dfrac{8}{23}\\
=(49-14)+\left ( \dfrac{8}{23}-\dfrac{8}{23} \right )-\dfrac{167}{32}\\
=35-\dfrac{167}{32}\\
=\dfrac{1120}{32}-\dfrac{167}{32}=\dfrac{953}{32}\\
B=71\dfrac{38}{45}-\left ( 43\dfrac{8}{45}-1\dfrac{17}{57} \right )\\
=71\dfrac{38}{45}- 43\dfrac{8}{45}+1\dfrac{17}{57} \\
=(71-43)+\left ( \dfrac{38}{45}-\dfrac{8}{45} \right )+\dfrac{74}{57}\\
=28+\dfrac{30}{45}+\dfrac{74}{57}\\
=28+\dfrac{2}{3}+\dfrac{74}{57}\\
=\dfrac{28.57}{57}+\dfrac{2.19}{3.19}+\dfrac{74}{57}\\
=\dfrac{1708}{57}\\
2)
a)\dfrac{7}{3}+\dfrac{2}{5}.\dfrac{5}{6}\\
=\dfrac{7}{3}+\dfrac{1}{3}=\dfrac{8}{3}\\
b)\dfrac{2}{3}-\dfrac{7}{3}:2\dfrac{4}{5}\\
=\dfrac{2}{3}-\dfrac{7}{3}:\dfrac{14}{5}\\
=\dfrac{2}{3}-\dfrac{7}{3}.\dfrac{5}{14}\\
=\dfrac{2}{3}-\dfrac{5}{6}\\
=\dfrac{4}{6}-\dfrac{5}{6}\\
=\dfrac{-1}{6}\\
c)\left ( \dfrac{3}{8}+\dfrac{1}{4} \right ):\left ( \dfrac{4}{3}-\dfrac{1}{6} \right )\\
=\left ( \dfrac{3}{8}+\dfrac{2}{8} \right ):\left ( \dfrac{8}{6}-\dfrac{1}{6} \right )\\
=\dfrac{5}{8}:\dfrac{7}{6}\\
=\dfrac{5}{8}.\dfrac{6}{7}\\
=\dfrac{15}{28}\\
3)
a)\dfrac{-4}{9}.\dfrac{7}{5}+\dfrac{4}{9}.\dfrac{8}{15}\\
=\dfrac{4}{9}.\left ( \dfrac{-7}{5}+\dfrac{8}{15} \right )\\
=\dfrac{4}{9}.\left ( \dfrac{-21}{15}+\dfrac{8}{15} \right )\\
=\dfrac{4}{9}.\dfrac{-13}{15}\\
=\dfrac{-52}{135}\\
b)2\dfrac{13}{27}-\dfrac{7}{15}+3\dfrac{14}{27}-\dfrac{8}{15}\\
=\left ( 2\dfrac{13}{27}+3\dfrac{14}{27} \right )+\left ( \dfrac{-7}{15}-\dfrac{8}{15} \right )\\
=(2+3)+\left ( \dfrac{13}{27}+\dfrac{14}{27} \right )+\dfrac{-15}{15}\\
=5+1-1\\
=5$