Cách làm cho bạn:
a) $\frac{2}{5} + \frac{3}{8} - \frac{7}{20} = (\frac{8}{10} - \frac{7}{20}) + \frac{3}{8} = \frac{1}{20} + \frac{3}{8} = \frac{2}{40} + \frac{15}{40} = \frac{17}{40}$;
b) $\frac{-5}{14} + \frac{3}{8} - \frac{1}{2} = \frac{-20}{56} + \frac{21}{56} - \frac{28}{56} = \frac{-20 + 21 -28}{56} = \frac{-27}{56}$;
c) $\frac{-1}{4} - \frac{5}{6} - \frac{11}{18} = \frac{-9}{36} - \frac{30}{36} - \frac{22}{18} = \frac{61}{36}$;
d) $\frac{1}{4} + \frac{7}{12} - \frac{7}{13} - \frac{7}{8} = \frac{78}{312} + \frac{182}{312} - \frac{168}{312} - \frac{273}{312} = \frac{-181}{312}$;
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