Giải bài 4 trang 27 SGK Toán 7 tập 1 - Chân trời sáng tạo

Đề bài

Tính giá trị các biểu thức sau:

a)$A = \left[ {\left( { - 0,5} \right) - \frac{3}{5}} \right]:\left( { - 3} \right) + \frac{1}{3} - \left( { - \frac{1}{6}} \right):\left( { - 2} \right)$

b)$B = \left( {\frac{2}{{25}} - 0,036} \right):\frac{{11}}{{50}} - \left[ {\left( {3\frac{1}{4} - 2\frac{4}{9}} \right)} \right].\frac{9}{{29}}$

Lời giải chi tiết

a)

$\begin{array}{l}A = \left[ {\left( { - 0,5} \right) - \frac{3}{5}} \right]:\left( { - 3} \right) + \frac{1}{3} - \left( { - \frac{1}{6}} \right):\left( { - 2} \right)\\ = \left( {\frac{{ - 5}}{{10}} - \frac{6}{{10}}} \right).\frac{{ - 1}}{3} + \frac{1}{3} - \frac{-1}{6}.\frac{{ - 1}}{2}\\ = \frac{{ - 11}}{{10}}.\frac{{ - 1}}{3} + \frac{1}{3} - \frac{1}{12}\\ = \frac{{11}}{{30}} + \frac{1}{3} + \frac{{ - 1}}{{12}}\\ = \frac{{22}}{{60}} + \frac{{20}}{{60}} - \frac{{ 5}}{{60}}\\ = \frac{{37}}{{60}}\end{array}$

b)

$\begin{array}{l}B = \left( {\frac{2}{{25}} - 0,036} \right):\frac{{11}}{{50}} - \left[ {\left( {3\frac{1}{4} - 2\frac{4}{9}} \right)} \right].\frac{9}{{29}}\\ = \left( {\frac{2}{{25}} - \frac{{36}}{{1000}}} \right).\frac{{50}}{{11}} - \left[ {\left( {\frac{{13}}{4} - \frac{{22}}{9}} \right)} \right].\frac{9}{{29}}\\ = \left( {\frac{{10}}{{125}} - \frac{9}{{250}}} \right).\frac{{50}}{{11}} - \left[ {\left( {\frac{{117}}{{36}} - \frac{{88}}{{36}}} \right)} \right].\frac{9}{{29}}\\ = \frac{{ 11}}{{250}}.\frac{{50}}{{11}} - \frac{{29}}{{36}}.\frac{9}{{29}}\\ = \frac{{ 1}}{{5}} - \frac{1}{4}\\ = \frac{{ 4}}{{20}} - \frac{{5}}{{20}}\\ = \frac{{ - 1}}{{20}}\end{array}$