Đề bài
Tính :
\(\eqalign{ & a){2 \over 3} + {3 \over 8} - {5 \over {12}} \cr & b){{ - 3} \over {14}} + {3 \over 8} - {1 \over 4} \cr & c){5 \over 9}.\left( {{3 \over 5} + {3 \over {10}}} \right) \cr & d){1 \over 3} + {3 \over 4} - {7 \over {18}} \cr & e){1 \over 4} + {7 \over {12}} - {1 \over {11}} - {5 \over 8} \cr & f)\left( {{1 \over 5} + {3 \over {10}}} \right):\left( { - 2{1 \over 3}} \right). \cr} \)
Lời giải chi tiết
\(\eqalign{ & a){2 \over 3} + {3 \over 8} - {5 \over {12}} = {{16} \over {24}} + {9 \over {24}} - {{10} \over {24}} = {{16 + 9 - 10} \over {24}} = {{15} \over {24}} = {5 \over 8} \cr & b){{ - 3} \over {14}} + {3 \over 8} - {1 \over 4} = {{ - 12} \over {56}} + {{21} \over {56}} - {{14} \over {56}} = {{ - 12 + 21 - 14} \over {56}} = {{ - 5} \over {56}} \cr & c){5 \over 9}.\left( {{3 \over 5} + {3 \over {10}}} \right) = {5 \over 9}.\left( {{6 \over {10}} + {3 \over {10}}} \right) = {5 \over 9}.{9 \over {10}} = {1 \over 2} \cr & d){1 \over 3} + {3 \over 4} - {7 \over {18}} = {{12} \over {36}} + {{27} \over {36}} - {{14} \over {36}} = {{12 + 27 - 14} \over {36}} = {{25} \over {36}} \cr & e){1 \over 4} + {7 \over {12}} - {1 \over {11}} - {5 \over 8} = {{66} \over {264}} + {{154} \over {264}} - {{24} \over {264}} - {{165} \over {264}} = {{66 + 154 - 24 - 165} \over {264}} = {{31} \over {264}} \cr & f)\left( {{1 \over 5} + {3 \over {10}}} \right):\left( { - 2{1 \over 3}} \right) = \left( {{2 \over {10}} + {3 \over {10}}} \right):\left( {{{ - 7} \over 3}} \right) = {5 \over {10}}.{{( - 3)} \over 7} = {{ - 3} \over {14}}. \cr} \)
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