Giải bài 6 trang 92 vở thực hành Toán 6 Q2

Đề bài

Bài 6. Tính giá trị của các biểu thức sau (tính hợp lí, nếu có thể):

a) \(\frac{{ - 3}}{7}.\frac{2}{5} + \frac{2}{5}.\left( { - \frac{5}{{14}}} \right) - \frac{{18}}{{35}}\)

b) \(\left( {\frac{2}{3} - \frac{5}{{11}} + \frac{1}{4}} \right):\left( {1 + \frac{5}{{12}} - \frac{7}{{11}}} \right)\)

c) \(\left( {13,6 - 37,8} \right).\left( { - 3,2} \right)\)

d) \(\left( { - 25,4} \right).\left( {18,5 + 43,6 - 16,8} \right):12,7\)

Lời giải chi tiết

a)

\(\begin{array}{l}\frac{{ - 3}}{7}.\frac{2}{5} + \frac{2}{5}.\left( { - \frac{5}{{14}}} \right) - \frac{{18}}{{35}} = \frac{2}{5}.\left[ {\frac{{ - 3}}{7} + \left( { - \frac{5}{{14}}} \right)} \right] - \frac{{18}}{{35}}\\ = \frac{2}{5}.\left( { - \frac{{11}}{{14}}} \right) - \frac{{18}}{{35}} =  - \frac{{11}}{{35}} - \frac{{18}}{{35}} =  - \frac{{29}}{{35}}\end{array}\)

b)

\(\begin{array}{l}\left( {\frac{2}{3} - \frac{5}{{11}} + \frac{1}{4}} \right):\left( {1 + \frac{5}{{12}} - \frac{7}{{11}}} \right) = \left( {\frac{{88}}{{132}} - \frac{{60}}{{132}} + \frac{{33}}{{132}}} \right):\left( {\frac{{132}}{{132}} + \frac{{55}}{{132}} - \frac{{84}}{{132}}} \right)\\ = \frac{{61}}{{132}}:\frac{{103}}{{132}} = \frac{{61}}{{103}}\end{array}\)

c) \(\left( {13,6 - 37,8} \right).\left( { - 3,2} \right) = \left( { - 24,2} \right).\left( { - 3,2} \right) = 77,44\)

d) \(\left( { - 25,4} \right).\left( {18,5 + 43,6 - 16,8} \right):12,7 = \left( { - 25,4} \right).45,3:12,7 =  - 90,6\)