Tính hợp lý a) -(3/10 - 6/11) - (21/30 - 5/11) b) (13/5 + 7/16) - (11/16 - 12/10)

* Hướng dẫn giải

a) 

$\begin{array}{l}-\left(\frac{3}{10}-\frac{6}{11}\right)-\left(\frac{21}{30}-\frac{5}{11}\right)\\ =-\frac{3}{10}+\frac{6}{11}-\frac{7}{10}+\frac{5}{11}\\ =\left(-\frac{3}{10}-\frac{7}{10}\right)+\left(\frac{6}{11}+\frac{5}{11}\right)\\ =-1+1=0\end{array}$

b) 

$\begin{array}{l}\left(\frac{13}{5}+\frac{7}{16}\right)-\left(\frac{11}{16}-\frac{12}{10}\right)\\ =\frac{13}{5}+\frac{7}{16}-\frac{11}{16}+\frac{6}{5}\\ =\left(\frac{13}{5}+\frac{6}{5}\right)+\left(\frac{7}{16}-\frac{11}{16}\right)\\ =\frac{19}{5}+\frac{-1}{4}=\frac{76}{20}+\frac{-5}{20}=\frac{71}{20}\end{array}$