Thực hiện phép tính (tính hợp lí nếu có thể): a) (34,72 + 32,28) : 5 – (57,25 – 36,05) : 2

Hướng dẫn giải:

a) (34,72 + 32,28) : 5 – (57,25 – 36,05) : 2;

= 67 : 5 + 21,2 : 2

= 13,4 – 10,6

= 2,8

b) \(8\frac{2}{7} - \left( {3\frac{4}{9} + 4\frac{2}{7}} \right)\);

\( = 8\frac{2}{7} - 3\frac{4}{9} - 4\frac{2}{7}\)

\( = \left( {8\frac{2}{7} - 4\frac{2}{7}} \right) - 3\frac{4}{9}\)

\( = \left[ {\left( {8 + \frac{2}{7}} \right) - \left( {4 + \frac{2}{7}} \right)} \right] - \left( {3 + \frac{4}{9}} \right)\)

\( = \left[ {\left( {8 - 4} \right) + \left( {\frac{2}{7} - \frac{2}{7}} \right)} \right] - \left( {3 + \frac{4}{9}} \right)\)

 \( = 4 - 3 - \frac{4}{9}\)

\( = 1 - \frac{4}{9}\)

\( = \frac{9}{9} - \frac{4}{9}\)

\( = \frac{5}{9}\)

c) \(\frac{5}{{13}} + \frac{{ - 5}}{7} + \frac{{ - 20}}{{41}} + \frac{8}{{13}} + \frac{{ - 21}}{{41}}\)

\( = \left( {\frac{5}{{13}} + \frac{8}{{13}}} \right) + \left( {\frac{{ - 20}}{{41}} + \frac{{ - 21}}{{41}}} \right) + \frac{{ - 5}}{7}\)

\( = \frac{{13}}{{13}} + \frac{{ - 41}}{{41}} + \frac{{ - 5}}{7}\)

\( = 1 + \left( { - 1} \right) + \frac{{ - 5}}{7}\)

\( = 0 + \frac{{ - 5}}{7}\)

\( = \frac{{ - 5}}{7}\).

d) \(1\frac{{13}}{{15}}.0,75 - \left( {\frac{8}{{15}} + 25\% } \right)\)

\( = \frac{{28}}{{15}}.\frac{{75}}{{100}} - \left( {\frac{8}{{15}} + \frac{{25}}{{100}}} \right)\)

\[ = \frac{{4.7}}{{3.5}}.\frac{{3.25}}{{4.25}} - \left( {\frac{8}{{15}} + \frac{1}{4}} \right)\]

\( = \frac{7}{5} - \frac{8}{{15}} - \frac{1}{4}\)

\( = \frac{{84}}{{60}} - \frac{{32}}{{60}} - \frac{{15}}{{60}}\)

\( = \frac{{37}}{{60}}\)