Bài 8 trang 57 Tài liệu dạy – học toán 6 tập 2: Tính :...

Tính :

$\eqalign{  & a)\left( { - 3,2} \right).{{ - 15} \over {64}} + \left( {0,8 - 2{4 \over {15}}} \right):3{2 \over 3}  \cr  & b)\left( { - 6,17 + 3{5 \over 9} - 2{{36} \over {97}}} \right).\left( {{1 \over 3} - 0,25 - {1 \over {12}}} \right). \cr}$

$\eqalign{  & a)( - 3,2).{{ - 15} \over {64}} + \left( {0.8 - 2{4 \over {15}}} \right):3{2 \over 3} = {{ - 32} \over {10}}.{{ - 15} \over {64}} + \left( {{8 \over {10}} - {{34} \over {15}}} \right):{{11} \over 3} = {3 \over 4} + \left( {{4 \over 5} - {{34} \over 5}} \right):{{11} \over 3}  \cr  &  = {3 \over 4} + \left( {{{12} \over {15}} - {{34} \over {15}}} \right):{{11} \over 3} = {3 \over 4} + {{ - 22} \over {15}}.{3 \over {11}} = {3 \over 4} + {{ - 2} \over 5} = {{15} \over {20}} + {{ - 8} \over {20}} = {7 \over {20}}  \cr  & b)\left( { - 6,17 + 3{5 \over 9} - 2{{36} \over {97}}} \right).\left( {{1 \over 3} = 0,25 - {1 \over {12}}} \right) = \left( { - 6,17 + 3{5 \over 9} - 2{{36} \over {97}}} \right).\left( {{1 \over 3} - {1 \over 4} - {1 \over {12}}} \right)  \cr  &  = \left( { - 6,17 + 3{5 \over 9} - 2{{36} \over {97}}} \right).\left( {{4 \over {12}} - {3 \over {12}} - {1 \over {12}}} \right) = \left( { - 6,17 + 3{5 \over 9} - 2{{36} \over {97}}} \right).{0 \over {12}}  \cr  &  = \left( { - 6,17 + 3{5 \over 9} - 2{{36} \over {97}}} \right).0 = 0 \cr}$