Bài 1 trang 88 sgk toán 7 tập 2
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})
( = {{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})