Đề bài

Tính giá trị các biểu thức sau: \(\begin{array}{l}a)A = (\frac{2}{3} + \frac{1}{5} - \frac{4}{9}):(\frac{1}{3} + \frac{2}{5} - \frac{6}{9})\\b)B = \frac{1}{2}.\frac{3}{5} + \frac{4}{7}:\frac{4}{5} - \frac{1}{{70}}\end{array}\)

Lời giải chi tiết

\(\begin{array}{l}a)A = (\frac{2}{3} + \frac{1}{5} - \frac{4}{9}):(\frac{1}{3} + \frac{2}{5} - \frac{6}{9})\\ = (\frac{{30}}{{45}} + \frac{9}{{45}} - \frac{{20}}{{45}}):(\frac{{15}}{{45}} + \frac{{18}}{{45}} - \frac{{30}}{{45}})\\ = \frac{{19}}{{45}}:\frac{3}{{45}}\\ = \frac{{19}}{{45}}.\frac{{45}}{3}\\ = \frac{{19}}{3}\\b)B = \frac{1}{2}.\frac{3}{5} + \frac{4}{7}:\frac{4}{5} - \frac{1}{{70}}\\ = \frac{3}{{10}} + \frac{4}{7}.\frac{5}{4} - \frac{1}{{70}}\\ = \frac{3}{{10}} + \frac{5}{7} - \frac{1}{{70}}\\ = \frac{{21}}{{70}} + \frac{{50}}{{70}} - \frac{1}{{70}}\\ = \frac{{70}}{{70}}\\ = 1\end{array}\)