Bài 99. Tính giá trị của các biểu thức sau:
\(P = \left( {0,5 - {3 \over 5}} \right):\left( { - 3} \right) + {1 \over 3} - \left( { - {1 \over 6}} \right):\left( { - 2} \right)\)
\(Q = \left( {{2 \over {25}} - 1,008} \right):{4 \over 7}:\left[ {\left( {3{1 \over 4} - 6{5 \over 9}} \right):2{2 \over {17}}} \right]\)
\(P = \left( {0,5 - {3 \over 5}} \right):\left( { - 3} \right) + {1 \over 3} - \left( { - {1 \over 6}} \right):\left( { - 2} \right)\)
\( = \left( { - {1 \over 2} - {3 \over 5}} \right):\left( { - 3} \right) + {1 \over 3} - \left( { - {1 \over 6}} \right).\left( { - {1 \over 2}} \right)\)
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\( = \left( {{{ - 5 - 6} \over {10}}} \right):\left( { - 3} \right) + {1 \over 3} - {1 \over {12}} = {{ - 11} \over {10}}:\left( { - 3} \right) + {1 \over 4}\)
\( = {{ - 11} \over {10}}.\left( { - {1 \over 3}} \right) + {1 \over 4} = {{11} \over {30}} + {1 \over 4} = {{37} \over {60}}\)
\(Q = \left( {{2 \over {25}} - 1,008} \right):{4 \over 7}:\left[ {\left( {3{1 \over 4} - 6{5 \over 9}} \right):2{2 \over {17}}} \right]\)
\( = \left( {{2 \over {25}} - {{126} \over {125}}} \right):{4 \over 7}:\left[ {\left( {{{13} \over 4} - {{59} \over 9}} \right).{{36} \over {17}}} \right]\)
\( = {{ - 116} \over {125}}.{7 \over 4}:\left( {{{ - 119} \over {36}}.{{36} \over {17}}} \right)\)
\(= {{ - 29.7} \over {125}}:\left( { - 7} \right) = {{29} \over {125}}\)