Đề bài

Tính một cách hợp lí: a)\(\frac{2}{9}+ \frac{-3}{10}+ \frac{-7}{10}\) b)\(\frac{-11}{6}+ \frac{2}{5}+ \frac{-1}{6}\) c)\(\frac{-5}{8} +\frac{12}{7}+\frac{13}{8}+\frac{2}{7}\)

Lời giải chi tiết

a)\(\frac{2}{9}+ \frac{-3}{10}+ \frac{-7}{10}=\frac{2}{9}+(\frac{-3}{10}+ \frac{-7}{10})= \frac{2}{9} + \frac{-10}{10}\)\(=\frac{2}{9}+ (-1)= \frac{2}{9} + \frac{-9}{9}=\frac{-7}{9}\) b)\(\frac{-11}{6}+ \frac{2}{5}+ \frac{-1}{6}= (\frac{-11}{6}+\frac{-1}{6})+\frac{2}{5}= \frac{-12}{6}+\frac{2}{5}\)\(=(-2)+\frac{2}{5}= \frac{-10}{5}+ \frac{2}{5}= \frac{-8}{5}\) c)\(\frac{-5}{8} +\frac{12}{7}+\frac{13}{8}+\frac{2}{7}= (\frac{-5}{8}+\frac{13}{8}) + (\frac{12}{7}+\frac{2}{7})\)= \(\frac{8}{8}+\frac{14}{7}= 1 +2 =3\)

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