Đề bài
Thực hiện phép tính :
a] \[{4 \over 5} + {{ - 2} \over {15}}\] b] \[{{ - 3} \over 5} + {5 \over 7}\]
c] \[{4 \over {21}}.{{ - 7} \over 8}\] d] \[{{ - 21} \over {24}}:{{ - 14} \over 8}\]
e] \[{2 \over 3} - {5 \over 7}.{{14} \over {25}}\] f] \[\left[ {{5 \over {12}} + {{ - 1} \over 4} + {3 \over 8}} \right].{3 \over 2}\]
g] \[\left[ {{1 \over 2} + {1 \over 3} + {2 \over 5}} \right]:\left[ { - 22{1 \over 5}} \right]\].
Lời giải chi tiết
\[\eqalign{ & a]{4 \over 5} + {{ - 2} \over {15}} = {{12} \over {15}} + {{ - 2} \over {15}} = {{10} \over {15}} = {2 \over 3} \cr & b]{{ - 3} \over 5} + {5 \over 7} = {{ - 21} \over {35}} + {{25} \over {35}} = {4 \over {35}} \cr & c]{4 \over {21}}.{{ - 7} \over 8} = {{4.[ - 7]} \over {21.8}} = {{ - 1} \over 6} \cr & d]{{ - 21} \over {24}}:{{ - 14} \over 8} = {{ - 21} \over {24}}.{{[ - 8]} \over {14}} = {1 \over 2} \cr & e]{2 \over 3} - {5 \over 7}.{{14} \over {25}} = {2 \over 3} - {{5.14} \over {7.25}} = {2 \over 3} - {2 \over 5} = {{10} \over {15}} - {6 \over {15}} = {4 \over {15}} \cr & f]\left[ {{5 \over {12}} + {{ - 1} \over 4} + {3 \over 8}} \right].{3 \over 2} = \left[ {{{10} \over {24}} + {{ - 6} \over {24}} + {9 \over {24}}} \right].{3 \over 2} = {{13} \over {24}}.{3 \over 2} = {{13} \over {16}} \cr & g]\left[ {{1 \over 2} + {1 \over 3} + {2 \over 5}} \right]:\left[ { - 22{1 \over 5}} \right] = \left[ {{{15} \over {30}} + {{10} \over {30}} + {{12} \over {30}}} \right]:\left[ {{{ - 111} \over 5}} \right] = {{37} \over {30}}.{{ - 5} \over {111}} = {{ - 1} \over {18}}. \cr} \]