Giải bài 2 trang 71 SGK Toán 6 Cánh diều

Đề bài

Tính một cách hợp lí:

a) \(\left( {\frac{{617}}{{191}} + \frac{{29}}{{33}} - \frac{{115}}{{117}}} \right).\left( {\frac{1}{4}+ \frac{-1}{5} - \frac{1}{{20}}} \right);\)

b) \(\frac{{12}}{5}.\left( {\frac{{-10}}{3} - \frac{5}{{12}}} \right)\);

c) \(1,23 - 5,48 + 8,77 - 4,32;\)

d) \(7.{\rm{ }}0,25{\rm{ }} + {\rm{ }}9.(-0,25)\).

Lời giải chi tiết

a)

 \(\begin{array}{l}\left( {\frac{{617}}{{191}} + \frac{{29}}{{33}} - \frac{{115}}{{117}}} \right).\left( {\frac{1}{4} + \frac{-1}{5} - \frac{1}{{20}}} \right)\\ = \left( {\frac{{617}}{{191}} + \frac{{29}}{{33}} - \frac{{115}}{{117}}} \right).\left( {\frac{5}{{20}} + \frac{-4}{{20}} - \frac{1}{{20}}} \right)\\ = \left( {\frac{{617}}{{191}} + \frac{{29}}{{33}} - \frac{{115}}{{117}}} \right).0\\ = 0\end{array}\)

b)

\(\begin{array}{l}\frac{{12}}{5}.\left( {\frac{{-10}}{3} - \frac{5}{{12}}} \right)\\ = \frac{{12}}{5}.\left( {\frac{{-40}}{{12}} - \frac{5}{{12}}} \right)\\ = \frac{{12}}{5}.\frac{{-45}}{{12}}\\ = -9\end{array}\)

c)

\(\begin{array}{l}1,23 - 5,48 + 8,77 - 4,32\\ = \left( {1,23 + 8,77} \right) - \left( {5,48 + 4,32} \right)\\ = 10 - 9,8\\ = 0,2\end{array}\)

d)

\(\begin{array}{l}7.{\rm{ }}0,25{\rm{ }} + {\rm{ }}9.(-0,25)\\=7 . 0,25 - 9. 0,25\\ = 0,25.\left( {7 - 9} \right)\\ = 0,25.(-2)\\ = -0,5 \end{array}\)