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Thực hiện các phép tính:
a) \(9,6.2{1 \over 2} – \left( {2.125 – 1{5 \over {12}}} \right):{1 \over 4}\)
b) \({5 \over {18}} – 1,456:{7 \over {25}} + 4,5.{4 \over 5}\);
c) \(\left( {{1 \over 2} + 0,8 – 1{1 \over 3}} \right).\left( {2,3 + 4{7 \over {25}} – 1,28} \right)\)
d) \(\left( { – 5} \right).12:\left[ {\left( { – {1 \over 4}} \right) + {1 \over 2}:\left( { – 2} \right)} \right] + 1{1 \over 3}\).
Hướng dẫn làm bài:
a) \(9,6.2{1 \over 2} – \left( {2.125 – 1{5 \over {12}}} \right):{1 \over 4}\)
\( = 9,6.{5 \over 2} – \left( {250 – {{17} \over {12}}} \right) \times 4\)
\( = 4,8.5 – \left( {1000 – {{17} \over 3}} \right)\)
\( = 24 – 1000 + {{17} \over 3}\)
\( = – 976 + {{17} \over 3}\)
\( = – 970{1 \over 3}\)
b) \({5 \over {18}} – 1,456:{7 \over {25}} + 4,5.{4 \over 5}\);
\( = {5 \over {18}} – 1,456 \times {{25} \over 7} + {9 \over 2}.{4 \over 5}\)
\( = {5 \over {18}} – 0,208 \times 25 + {{18} \over 5}\)
\( = {5 \over {18}} – 5,2 + {{18} \over 5}\)
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\( = {{25 – 468 + 324} \over {90}}\)
\( = {{ – 119} \over {90}}\)
c) \(\left( {{1 \over 2} + 0,8 – 1{1 \over 3}} \right).\left( {2,3 + 4{7 \over {25}} – 1,28} \right)\)
\( = \left( {{1 \over 2} + {4 \over 5} – {4 \over 3}} \right).\left( {{{23} \over {10}} + {{107} \over {25}} – {{32} \over {25}}} \right)\)
\( = \left( {{{15 + 24 – 40} \over {30}}} \right).\left( {{{23} \over {10}} + {{107} \over {25}} – {{32} \over {25}}} \right)\)
\( = \left( {{{15 + 24 – 40} \over {30}}} \right).\left( {{{115 + 214 – 64} \over {50}}} \right)\)
\( = {{ – 1} \over {30}}.{{265} \over {50}}\)
\( = {{ – 53} \over {300}}\)
d) \(\left( { – 5} \right).12:\left[ {\left( { – {1 \over 4}} \right) + {1 \over 2}:\left( { – 2} \right)} \right] + 1{1 \over 3}\)
\( = – 60:\left[ {{1 \over 4} + {1 \over 2} \times \left( {{{ – 1} \over 2}} \right)} \right] + 1.{1 \over 3}\)
\( = – 60:\left[ { – {1 \over 4} – {1 \over 4}} \right] + 1{1 \over 3}\)
\( = – 60:\left( {{1 \over 2}} \right) + 1{1 \over 3}\)
\( = 120 + 1{1 \over 3}\)
\( = 121{1 \over 3}\)