PHẦN II. TỰ LUẬN (7,0 điểm)

(1,5 điểm) Tính giá trị của các biểu thức sau (tính hợp lí nếu có thể):

a) \(\frac{1}{2} - \frac{2}{{ - 3}} + \frac{3}{4}\);  

b) \(\sqrt {\frac{{25}}{{64}}} - \left| { - \frac{7}{8}} \right|:\frac{1}{3}\);      

c) \(\left( {\frac{1}{6} - \frac{5}{8}} \right).2\frac{1}{3} + \left( {\frac{5}{6} + \frac{{21}}{8}} \right):\frac{3}{7}\).

a) \(\frac{1}{2} - \frac{2}{{ - 3}} + \frac{3}{4} = \frac{1}{2} + \frac{2}{3} + \frac{3}{4} = \frac{6}{{12}} + \frac{8}{{12}} + \frac{9}{{12}} = \frac{{23}}{{12}}\).

b) \(\sqrt {\frac{{25}}{{64}}} - \left| { - \frac{7}{8}} \right|:\frac{1}{3} = \frac{5}{8} - \frac{7}{8}.\frac{3}{1} = \frac{5}{8} - \frac{{21}}{8} = \frac{{ - 16}}{8} = - 2\).

c) \[\left( {\frac{1}{6} - \frac{5}{8}} \right).2\frac{1}{3} + \left( {\frac{5}{6} + \frac{{21}}{8}} \right):\frac{3}{7} = \left( {\frac{1}{6} - \frac{5}{8}} \right).\frac{7}{3} + \left( {\frac{5}{6} + \frac{{21}}{8}} \right).\frac{7}{3}\]

\[ = \left( {\frac{1}{6} + \frac{5}{6} - \frac{5}{8} + \frac{{21}}{8}} \right).\frac{7}{3} = \left( {\frac{6}{6} + \frac{{16}}{8}} \right).\frac{7}{3} = \left( {1 + 2} \right).\frac{7}{3} = 7\].