Bài tập về thực hiện phép tính.

1.

M = $\frac{-3}{8}.1\frac{3}{5}+\frac{1}{7}\left ( -1\frac{1}{6} \right )$

  = $\frac{-3}{8}.\frac{8}{5}+\frac{1}{7}.\frac{-7}{6}$

  = $\frac{-3}{5}+\frac{-1}{6}$

  = $\frac{-23}{30}$

N = $2\frac{1}{3}.\left ( -3\frac{1}{4} \right ).(-2,5)$

  = $\frac{7}{3}.\frac{-13}{4}.\frac{-5}{2}$

  = $\frac{455}{24}$

P = $\left ( \frac{3}{5}-0,2 \right ).\left ( 0,5-\frac{4}{5} \right )$

  = $\left ( \frac{3}{5}-\frac{1}{5} \right ).\left ( \frac{1}{2}-\frac{4}{5} \right )$

  = $\frac{2}{5}.\frac{-3}{10}$

  = $\frac{-3}{25}$

Vậy M < P < N

2. 

a) A = $\left ( \frac{2}{7}.\frac{1}{4}-\frac{1}{3}.\frac{2}{7} \right ):\left ( \frac{2}{7}.\frac{3}{9}-\frac{2}{7}.\frac{2}{5} \right )$

     = $\left [\frac{2}{7}.\left ( \frac{1}{4}-\frac{1}{3} \right )  \right ]:\left [\frac{2}{7}.\left ( \frac{3}{9}-\frac{2}{5} \right )  \right ]$

     = $\frac{-1}{12}:\frac{-1}{15}$

     = $\frac{5}{4}$

b) B = $\frac{\left ( \frac{1}{5}-\frac{2}{7} \right ).\frac{3}{4}-\frac{3}{4}.\left ( \frac{1}{3}-\frac{2}{7} \right )}{\frac{1}{5}.\frac{2}{7}-\frac{1}{3}.\left ( \frac{2}{7}+\frac{3}{9} \right )+\frac{3}{9}.\frac{1}{5}}$

     = $\frac{\frac{3}{4}.\left ( \frac{1}{5}-\frac{2}{7}-\frac{1}{3}+\frac{2}{7} \right )}{\frac{1}{5}.\left (\frac{2}{7}+\frac{1}{3}  \right )-\frac{1}{3}.\left ( \frac{2}{7}+\frac{1}{3} \right )}$

     = $\frac{\frac{3}{4}.\left ( \frac{1}{5}-\frac{1}{3} \right )}{\left ( \frac{1}{5}-\frac{1}{3} \right ).\left ( \frac{2}{7}+\frac{1}{3} \right )}$

     = $\frac{63}{52}$

3. M = $\frac{1}{2}.\frac{1}{-3}+\frac{1}{-3}.\frac{1}{4}+\frac{1}{4}.\frac{1}{-5}+\frac{1}{-5}.\frac{1}{6}$

  = $-\left ( \frac{1}{2}.\frac{1}{3}+\frac{1}{3}.\frac{1}{4}+\frac{1}{4}.\frac{1}{5}+\frac{1}{5}.\frac{1}{6} \right )$

  = $-\left ( \frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6} \right )$

  = $-\left ( \frac{1}{2}-\frac{1}{6} \right )$

  = $\frac{-1}{3}$