Bài 123 trang 60 SBT Toán 6 – Cánh Diều Tập 2: Tính một cách hợp lí: \(1, 6 + \left( {2, 7 - 0, 7. 6} \right) - \, \left( {94. 0, 7 - 99. 2, 7} \right);\) \(0...

Tính một cách hợp lí:

a) \(1,6 + \left( {2,7 - 0,7.6} \right) - \,\left( {94.0,7 - 99.2,7} \right);\)

b) \(0,1 - \,0,02 + 0,2 - 0,01 + 0,03 - 0,8\)

c) \(\left( {\frac{{ - 5}}{{116}} + \,\frac{{ - 117}}{{232}} - \frac{{71}}{{464}}} \right)\,.\,\left( {\frac{5}{6}\, - \frac{1}{2}\, - \,\frac{1}{3}} \right);\)

d) \(\left( {\frac{2}{{1.3}}\, + \,\frac{2}{{3.5}} + \frac{2}{{5.7}}} \right)\,.\,\left( {\frac{{10.13}}{3} - \frac{{{2^2}}}{3} - \frac{{{5^3}}}{3}} \right)\,\)

e) \(\frac{{2\;.\;4\;.\;10\; + \;4\;.\;6\;.\;8\; + \;14\;.\;16\;.\;20}}{{3\;.\;6\;.\;15\; + \;6\;.\;9\;.\;12\; + \;21\;.\;24\;.\;30}}\)

Áp dụng tính chất giao hoán, kết hợp, phân phối của phép nhân đối với phép cộng. Quy tắc dấu ngoặc

a)

\(\begin{array}{l}1,6 + \left( {2,7 - 0,7.6} \right) - \,\left( {94.0,7 - 99.2,7} \right)\\ = 1,6 + 2,7 - 0,7.6 - \,94.0,7 + 99.2,7\\ = 1,6 + \left( {2,7 + 99.2,7} \right) - \left( {0,7.6 + \,94.0,7} \right)\\ = 1,6 + 2,7.\left( {1 + 99} \right) - 0,7.\left( {6 + \,94} \right)\\ = 1,6 + 2,7.100 - 0,7.100\\ = 1,6 + 270 - 70\\ = 1,6 + \left( {270 - 70} \right)\\ = 1,6 + 200\\ = 201,6\end{array}\)

b)

\(\begin{array}{l}0,1 - \,0,02 + 0,2 - 0,01 + 0,03 - 0,8\\ = \left( {0,1 + 0,2 - 0,8} \right) + \left( {0,03 - \,0,02 - 0,01} \right)\\ = - 0,5 + 0\\ = - 0,5\end{array}\)

c)

\(\begin{array}{l}\left( {\frac{{ - 5}}{{116}} + \,\frac{{ - 117}}{{232}} - \frac{{71}}{{464}}} \right)\,.\,\left( {\frac{5}{6}\, - \frac{1}{2}\, - \,\frac{1}{3}} \right);\\ = \left( {\frac{{ - 5}}{{116}} + \,\frac{{ - 117}}{{232}} - \frac{{71}}{{464}}} \right)\,.\,\left( {\frac{5}{6}\, - \frac{{1.3}}{{2.3}}\, - \,\frac{{1.2}}{{3.2}}} \right)\\ = \left( {\frac{{ - 5}}{{116}} + \,\frac{{ - 117}}{{232}} - \frac{{71}}{{464}}} \right)\,.\,\left( {\frac{5}{6}\, - \frac{3}{6}\, - \,\frac{2}{6}} \right)\\ = \left( {\frac{{ - 5}}{{116}} + \,\frac{{ - 117}}{{232}} - \frac{{71}}{{464}}} \right)\,.\,\left( {\frac{{5 - 3 - 2}}{6}\,} \right)\\ = \left( {\frac{{ - 5}}{{116}} + \,\frac{{ - 117}}{{232}} - \frac{{71}}{{464}}} \right).0\\ = 0\end{array}\)

d)

\(\begin{array}{l}\left( {\frac{2}{{1.3}}\, + \,\frac{2}{{3.5}} + \frac{2}{{5.7}}} \right)\,.\,\left( {\frac{{10.13}}{3} - \frac{{{2^2}}}{3} - \frac{{{5^3}}}{3}} \right)\,\\ = \left( {\frac{1}{1} - \frac{1}{3} + \frac{1}{3} - \frac{1}{5} + \frac{1}{5} - \frac{1}{7}} \right).\left( {\frac{{10.13 - {2^2} - {5^3}}}{3}} \right)\\ = \left( {1 - \frac{1}{7}} \right).\frac{{130 - 4 - 125}}{3}\\ = \frac{6}{7}.\frac{1}{3}\\ = \frac{2}{7}\end{array}\)

e)

\(\begin{array}{l}\frac{{2\;.\;4\;.\;10\; + \;4\;.\;6\;.\;8\; + \;14\;.\;16\;.\;20}}{{3\;.\;6\;.\;15\; + \;6\;.\;9\;.\;12\; + \;21\;.\;24\;.\;30}}\\ = \frac{{2.2.2\left( {1\;.\;2\;.\;5\; + \;2\;.\;3\;.\;4\; + \;7\;.\;8\;.\;10} \right)}}{{3.3.3\left( {1\;.\;2\;.\;5\; + \;2\;.\;3\;.\;4\; + \;7\;.\;8\;.\;10} \right)}}\\ = \frac{8}{27}\end{array}\)