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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) \(\left( {{5 \over {12}} + {{ – 1} \over 4} + {3 \over 8}} \right).{3 \over 2}\)
Advertisements (Quảng cáo)
g) \(\left( {{1 \over 2} + {1 \over 3} + {2 \over 5}} \right):\left( { – 22{1 \over 5}} \right)\).
\(\eqalign{ & a){4 \over 5} + {{ – 2} \over {15}} = {{12} \over {15}} + {{ – 2} \over {15}} = {{10} \over {15}} = {2 \over 3} \cr & b){{ – 3} \over 5} + {5 \over 7} = {{ – 21} \over {35}} + {{25} \over {35}} = {4 \over {35}} \cr & c){4 \over {21}}.{{ – 7} \over 8} = {{4.( – 7)} \over {21.8}} = {{ – 1} \over 6} \cr & d){{ – 21} \over {24}}:{{ – 14} \over 8} = {{ – 21} \over {24}}.{{( – 8)} \over {14}} = {1 \over 2} \cr & e){2 \over 3} – {5 \over 7}.{{14} \over {25}} = {2 \over 3} – {{5.14} \over {7.25}} = {2 \over 3} – {2 \over 5} = {{10} \over {15}} – {6 \over {15}} = {4 \over {15}} \cr & f)\left( {{5 \over {12}} + {{ – 1} \over 4} + {3 \over 8}} \right).{3 \over 2} = \left( {{{10} \over {24}} + {{ – 6} \over {24}} + {9 \over {24}}} \right).{3 \over 2} = {{13} \over {24}}.{3 \over 2} = {{13} \over {16}} \cr & g)\left( {{1 \over 2} + {1 \over 3} + {2 \over 5}} \right):\left( { – 22{1 \over 5}} \right) = \left( {{{15} \over {30}} + {{10} \over {30}} + {{12} \over {30}}} \right):\left( {{{ – 111} \over 5}} \right) = {{37} \over {30}}.{{ – 5} \over {111}} = {{ – 1} \over {18}}. \cr} \)