Đáp án+Giải thích các bước giải:

 $a)\; \dfrac{2}{21}-\dfrac{-1}{28}=\dfrac{2}{21}+\dfrac{1}{28}=\dfrac{8}{84}+\dfrac{3}{84}=\dfrac{11}{84}$

 $a)\; \dfrac{-2}{33}+\dfrac{5}{55}=\dfrac{-2}{33}+\dfrac1{11}=\dfrac{-2}{33}+\dfrac{3}{33}=\dfrac1{33}$

 $a)\; \dfrac{-1}{39}+\dfrac{-1}{52}=\dfrac{-4}{156}+\dfrac{-3}{156}=\dfrac{-7}{156}$

 $a)\; \dfrac25+\dfrac{-4}3+\dfrac{-1}2=\dfrac{12}{30}+\dfrac{-40}{30}+\dfrac{-15}{30}=\dfrac{-43}{50}$

 $b)\; -4,75-1\dfrac{7}{12}=-\dfrac{19}4-\dfrac{19}{12}=-\dfrac{57}{12}-\dfrac{19}{12}=-\dfrac{76}{12}=-\dfrac{19}3$

 $b)\; 0,4-\dfrac45=\dfrac25-\dfrac{14}5=-\dfrac{12}5$

 $b)\; -1\dfrac14-(-2,25)=-\dfrac54+\dfrac94=1$

 $b)\; \dfrac{-7}{10}+\dfrac{6}{23}+\dfrac{17}{10}+\dfrac{17}{23}$

$= \left(\dfrac{-7}{10}+\dfrac{17}{10}\right)+\left(\dfrac{6}{23}+\dfrac{17}{23}\right)$

$= 1+1=2$

 $c)\; -\left(\dfrac35+\dfrac34\right)-\left(-\dfrac34+\dfrac25\right)$

$= -\dfrac35-\dfrac34+\dfrac34-\dfrac25$

$= -1$

 $c)\; -\left(\dfrac37+\dfrac38\right)-\left(-\dfrac38+\dfrac47\right)$

$= -\dfrac37-\dfrac38+\dfrac38-\dfrac47$

$= -1$

 $c)\; \dfrac{11}{15}+3\dfrac8{17}+\dfrac4{15}-2\dfrac8{17}$

$= 1+\dfrac8{17}=\dfrac{25}{17}$ 

 $c)\; \dfrac{5}{15}+\dfrac{14}{25}-\dfrac{12}9+\dfrac27+\dfrac{11}{25}$

$= \dfrac13-\dfrac43+\dfrac27+1$

$=-1+1+\dfrac27 = \dfrac27$

Đáp án+Giải thích các bước giải:

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