Thực hiện các phép tính :
a) \({4 \over 7}:\left( {{2 \over 3}.{8 \over 7}} \right)\) b) \({2 \over 7} + {5 \over 7}.{{14} \over {25}}\)
c) \({5 \over 9}:{{10} \over 3} - 1\) d) \( - {1 \over 2}.{4 \over 7} + {3 \over 7}:{{15} \over {14}}\).
\(\eqalign{ & a){4 \over 7}:\left( {{2 \over 3}.{8 \over 7}} \right) = {4 \over 7}:\left( {{{2.8} \over {3.7}}} \right) = {4 \over 7}:{{16} \over {21}} = {4 \over 7}.{{21} \over {16}} = {{4.21} \over {7.16}} = {{1.3} \over {1.4}} = {3 \over 4} \cr & b){2 \over 7} + {5 \over 7}.{{14} \over {25}} = {2 \over 7} + {{5.14} \over {7.25}} = {2 \over 7} + {2 \over 5} = {{10} \over {35}} + {{14} \over {35}} = {{24} \over {35}} \cr & c){5 \over 9}:{{10} \over 3} - 1 = {5 \over 9}.{3 \over {10}} - 1 = {{5.3} \over {9.10}} - 1 = {{1.1} \over {2.3}} - 1 = {1 \over 6} - {6 \over 6} = {{ - 5} \over 6} \cr & d) - {1 \over 2}.{4 \over 7} + {3 \over 7}:{{15} \over {14}} = {{( - 1).4} \over {2.7}} + {3 \over 7}.{{14} \over {15}} = {{( - 1).2} \over 7} + {{3.14} \over {7.15}} = {{ - 2} \over 7} + {2 \over 5} = {{ - 10} \over {35}} + {{14} \over {35}} = {4 \over {35}} \cr} \)