Giải bài 1 trang 8 vở thực hành Toán 7

Đề bài

Tính.

a, \(\frac{{ - 6}}{{18}} + \frac{{18}}{{27}};\)

b, \(2,5 - \left( { - \frac{6}{9}} \right);\)

c, \( - 0,32.\left( { - 0,875} \right);\)

d, \(\left( { - 5} \right):2\frac{1}{5}.\)

Lời giải chi tiết

a,                                                b,

 \(\begin{array}{l}\frac{{ - 6}}{{18}} + \frac{{18}}{{27}} = \frac{{ - 6:6}}{{18:6}} + \frac{{18:9}}{{27:9}}\\ = \frac{{ - 1}}{3} + \frac{2}{3} = \frac{1}{3}.\end{array}\)             \(\begin{array}{l}2,5 - \left( { - \frac{6}{9}} \right) = \frac{{2.2,5}}{{2.1}} - \left( { - \frac{{6:3}}{{9:3}}} \right)\\ = \frac{5}{2} + \frac{2}{3} = \frac{{15}}{6} + \frac{4}{6} = \frac{{19}}{6}.\end{array}\)

c

,\(\begin{array}{l} - 0,32.\left( { - 0,875} \right) = 0,32.0,875\\ = \frac{{32}}{{100}}.\frac{{875}}{{1000}} = \frac{{28000}}{{100000}} = 0,28.\end{array}\)

d, \(\left( { - 5} \right):2\frac{1}{5} =  - 5:\frac{{11}}{5} =  - 5.\frac{5}{{11}} = \frac{{ - 25}}{{11}}.\)