Bài tập 1 Tính giá trị của biểu thức sau : a/ 2/35 : ( 3/5+3/7) b/1,2.25/6-(4/3+5/3) c/5 5/7-(3/7+2 3/5):4/5 d/1,4.15/49-(4/5+2/3):2 1/5

Đáp án:

$\begin{array}{l}
a)\dfrac{2}{{35}}:\left( {\dfrac{3}{5} + \dfrac{3}{7}} \right)\\
 = \dfrac{2}{{35}}:\dfrac{{21 + 15}}{{35}}\\
 = \dfrac{2}{{35}}.\dfrac{{35}}{{36}}\\
 = \dfrac{1}{{18}}\\
b)1,2.\dfrac{{25}}{6} - \left( {\dfrac{4}{3} + \dfrac{5}{3}} \right)\\
 = \dfrac{6}{5}.\dfrac{{25}}{6} - \dfrac{9}{3}\\
 = 5 - 3\\
 = 2\\
c)5\dfrac{5}{7} - \left( {\dfrac{3}{7} + 2\dfrac{3}{5}} \right):\dfrac{4}{5}\\
 = \dfrac{{40}}{7} - \left( {\dfrac{3}{7} + \dfrac{{13}}{5}} \right).\dfrac{5}{4}\\
 = \dfrac{{40}}{7} - \dfrac{{15 + 91}}{{35}}.\dfrac{5}{4}\\
 = \dfrac{{40}}{7} - \dfrac{{106}}{{7.4}}\\
 = \dfrac{{40}}{7} - \dfrac{{53}}{7}\\
 = \dfrac{{ - 13}}{7}\\
d)1,4.\dfrac{{15}}{{49}} - \left( {\dfrac{4}{5} + \dfrac{2}{3}} \right):2\dfrac{1}{5}\\
 = \dfrac{7}{5}.\dfrac{{15}}{{49}} - \dfrac{{22}}{{15}}:\dfrac{{11}}{5}\\
 = \dfrac{3}{7} - \dfrac{{22}}{{15}}.\dfrac{5}{{11}}\\
 = \dfrac{3}{7} - \dfrac{2}{3}\\
 = \dfrac{{ - 5}}{{21}}
\end{array}$