Đáp án:
$\displaystyle \begin{array}{{>{\displaystyle}l}} Bài\ 1:\\ a.\ \frac{-4}{69} ;\ b.\ \frac{-4}{15} ;\ c.\ 3;\ d.\ \frac{-40}{9}\\ Bài\ 2:\\ a.\ \frac{-13}{245} ;\ b.\ \frac{5}{14} ;\ c.\ \frac{33}{5} ;\ d.\ 0 \end{array}$
Giải thích các bước giải:
$\displaystyle \begin{array}{{>{\displaystyle}l}} Bài\ 1:\\ a.\ ( -0,25) .\frac{4}{17} .\left( -3\frac{5}{21}\right) .\left(\frac{-7}{23}\right) =\frac{-1}{4} .\frac{4}{17} .\frac{-68}{21} .\frac{-7}{23}\\ =\frac{-4.17.4.7}{4.17.7.3.23} =\frac{-4}{3.23} =\frac{-4}{69}\\ b.\ \ \left( -\frac{2}{5}\right) .\frac{4}{15} +\left(\frac{-3}{10}\right) .\frac{4}{15} =\frac{4}{15} .\left(\frac{-2-3}{5}\right) =\frac{4}{15} .( -1) =\frac{-4}{15}\\ c.\ 21-3\frac{3}{4} :\left(\frac{3}{8} -\frac{1}{6}\right) =21-\frac{15}{4} :\left(\frac{9}{24} -\frac{4}{24}\right) =21-\frac{15}{4} .\frac{24}{5}\\ =21-18=3\\ d.\ \left( -\frac{5}{2} +\frac{2}{5}\right) :\frac{3}{8} +\left(\frac{4}{5} -\frac{11}{30}\right) :\frac{3}{8} =\left( -\frac{25}{10} +\frac{4}{10}\right) .\frac{8}{3} +\left(\frac{24}{30} -\frac{11}{30}\right) .\frac{8}{3}\\ =\frac{8}{3} .\left(\frac{-21}{10} +\frac{13}{30}\right) =\frac{8}{3} .\left(\frac{-63+13}{30}\right) =\frac{8}{3} .\frac{-50}{30} =\frac{-40}{9}\\ Bài\ 2:\\ a.\ ( -0,35) .\frac{3}{14} .\left( -3\frac{5}{7}\right) .\left( -\frac{4}{21}\right) =\frac{-7}{20} .\frac{3}{14} .\frac{-26}{7} .\frac{-4}{21}\\ =\frac{-7.3.26.4}{4.5.2.7.7.3.7} =\frac{-13}{245}\\ b.\ \left( -\frac{3}{7}\right) .\frac{5}{11} +\left(\frac{-5}{14}\right) .\frac{5}{11} =\frac{5}{11} .\left(\frac{-6}{14} +\frac{-5}{14}\right) =\frac{5}{11} .\frac{-11}{14} =\frac{5}{14}\\ c.\ 15-2\frac{1}{3} :\left(\frac{4}{9} -\frac{1}{6}\right) =15-\frac{7}{3} :\left(\frac{24-9}{54}\right) =15-\frac{7}{3} .\frac{54}{15} =15-\frac{42}{5}\\ =\frac{75-42}{5} =\frac{33}{5}\\ d.\ \left( -\frac{3}{4} +\frac{2}{5}\right) :\frac{3}{7} +\left(\frac{3}{5} +\frac{-1}{4}\right) :\frac{3}{7} =\frac{7}{3} .\left(\frac{-3}{4} +\frac{2}{5} +\frac{3}{5} +\frac{-1}{4}\right)\\ =\frac{7}{3} .( -1+1) =0 \end{array}$
