Giải bài 2 trang 8 vở thực hành Toán 7

Đề bài

Tính giá trị của các biểu thức sau:

a, \(\left( {8 + 2\frac{1}{3} – \frac{3}{5}} \right) – \left( {5 + 0,4} \right) – \left( {3\frac{1}{3} – 2} \right);\)

b, \(\left( {7 – \frac{1}{2} – \frac{3}{4}} \right):\left( {5 – \frac{1}{4} – \frac{5}{8}} \right).\)

Lời giải chi tiết

a,

       \(\begin{array}{l}\left( {8 + 2\frac{1}{3} – \frac{3}{5}} \right) – \left( {5 + 0,4} \right) – \left( {3\frac{1}{3} – 2} \right)\\ = \left( {8 + \frac{7}{3} – \frac{3}{5}} \right) – \left( {5 + \frac{2}{5}} \right) – \left( {\frac{{10}}{3} – 2} \right)\\ = \left( {\frac{{120}}{{15}} + \frac{{35}}{{15}} – \frac{9}{{15}}} \right) – \frac{{27}}{5} – \frac{4}{3}\\ = \frac{{146}}{{15}} – \frac{{81}}{{15}} – \frac{{20}}{{15}}\\ = \frac{{146 – 81 – 20}}{{15}} = \frac{{45}}{{15}} = 3.\end{array}\) 

b,       \(\begin{array}{l}\left( {7 – \frac{1}{2} – \frac{3}{4}} \right):\left( {5 – \frac{1}{4} – \frac{5}{8}} \right)\\ = \left( {\frac{{28}}{4} – \frac{2}{4} – \frac{3}{4}} \right):\left( {\frac{{40}}{8} – \frac{2}{8} – \frac{5}{8}} \right)\\ = \frac{{23}}{4}:\frac{{33}}{8}\\ = \frac{{23}}{4}.\frac{8}{{33}} = \frac{{46}}{{33}}.\end{array}\)