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Đáp án + Giải thích các bước giải:

 Bài 5:
a) $\dfrac{9}{17} . \dfrac{3}{7} + \dfrac{9}{17} : \dfrac{7}{4}$
$= \dfrac{9}{17} . \dfrac{3}{7} + \dfrac{9}{17} . \dfrac{4}{7}$
$= \dfrac{9}{17} . \bigg(\dfrac{3}{7} + \dfrac{4}{7}\bigg)$

$= \dfrac{9}{17} . \dfrac{7}{7}$

$= \dfrac{9}{17}$

b) $\bigg(\dfrac{-9}{25}\bigg) . 17\dfrac{2}{3} - \bigg(\dfrac{-3}{5}\bigg)^2 . \dfrac{22}{3}$

$= \bigg(\dfrac{-9}{25}\bigg) . \dfrac{53}{3} - \dfrac{9}{25} . \dfrac{22}{3}$

$= \dfrac{9}{25} . \dfrac{-53}{3} - \dfrac{9}{25} . \dfrac{22}{3}$

$= \dfrac{9}{25} . \bigg(\dfrac{-53}{3} - \dfrac{22}{3}\bigg)$

$= \dfrac{9}{25} . \dfrac{-75}{3}$

$= \dfrac{9}{25} . (-25)$

$= -9$

c) $\dfrac{6}{7} . \dfrac{8}{13} + \dfrac{6}{13} . \dfrac{9}{7} - \dfrac{4}{13} . \dfrac{6}{7}$
$= \dfrac{6}{17} . \dfrac{8}{13} +\dfrac{6}{7} . \dfrac{9}{13} - \dfrac{4}{13} . \dfrac{6}{7}$

$= \dfrac{6}{17} . \bigg(\dfrac{8}{13} + \dfrac{9}{13} - \dfrac{4}{13}\bigg)$
$= \dfrac{6}{17} . \dfrac{13}{13}$

$= \dfrac{6}{17}$

d) $\bigg(\dfrac{67}{111} + \dfrac{2}{33} - \dfrac{15}{117}\bigg)\bigg(\dfrac{1}{3} - 25\% - \dfrac{1}{12}\bigg)$

$= \bigg(\dfrac{67}{111} + \dfrac{2}{33} - \dfrac{15}{117}\bigg)\bigg(\dfrac{1}{3} - \dfrac{1}{4} - \dfrac{1}{12}\bigg)$
$= \bigg(\dfrac{67}{111} + \dfrac{2}{33} - \dfrac{15}{117}\bigg)\bigg(\dfrac{4}{12} - \dfrac{3}{12} - \dfrac{1}{12}\bigg)$

$= \bigg(\dfrac{67}{111} + \dfrac{2}{33} - \dfrac{15}{117}\bigg) . 0$

$= 0$