B. TỰ LUẬN (3,0 điểm)

Câu 25-26. (1,5 điểm)

1) Thực hiện phép tính (tính hợp lí nếu có thể):

a) \(\left( { - 2,4 + \frac{1}{3}} \right):3,1 + 75\% :1\frac{1}{2}.\)                                                    b) \(\frac{3}{4} \cdot 26\frac{2}{9} - 38\frac{2}{9} \cdot \frac{3}{4}.\)

1) a) \(\left( { - 2,4 + \frac{1}{3}} \right):3,1 + 75\% :1\frac{1}{2}\)

\[ = \left( { - \frac{{24}}{{10}} + \frac{1}{3}} \right):\frac{{31}}{{10}} + \frac{{75}}{{100}}:\frac{3}{2}\]

\[ = \left( { - \frac{{12}}{5} + \frac{1}{3}} \right) \cdot \frac{{10}}{{31}} + \frac{3}{4} \cdot \frac{2}{3}\]

\[ = \left( { - \frac{{36}}{{15}} + \frac{5}{{15}}} \right) \cdot \frac{{10}}{{31}} + \frac{1}{2}\]

\[ = \frac{{ - 31}}{{15}} \cdot \frac{{10}}{{31}} + \frac{1}{2}\]\[ = \frac{{ - 2}}{3} + \frac{1}{2}\]

\[ = \frac{{ - 4}}{6} + \frac{3}{6} = - \frac{1}{6}.\]

b) \(\frac{3}{4} \cdot 26\frac{2}{9} - 38\frac{2}{9} \cdot \frac{3}{4}\)

\( = \frac{3}{4} \cdot \left( {26\frac{2}{9} - 38\frac{2}{9}} \right)\)

\( = \frac{3}{4} \cdot \left( {26 + \frac{2}{9} - 38 - \frac{2}{9}} \right)\)

\( = \frac{3}{4} \cdot \left( { - 12} \right) = - 9.\)