Thực hiện phép tính (tính hợp lí nếu có thể). (a) 2 1 /5 + 0 , 25 . ( 2 /5 ) ^2 ;

a) \(2\frac{1}{5} + 0,25\,\,.\,\,{\left( {\frac{2}{5}} \right)^2} = \frac{{11}}{5} + \frac{1}{4}\,\,.\,\,\frac{4}{{25}} = \frac{{11}}{5} + \frac{1}{{25}} = \frac{{56}}{{25}}\);

b) \[\frac{{ - 3}}{{22}} + \frac{1}{9} + \frac{5}{{22}}\, + \frac{{ - 10}}{9} = \left( {\frac{{ - 3}}{{22}} + \frac{5}{{22}}} \right) + \left( {\frac{1}{9} + \frac{{ - 10}}{9}} \right) = \frac{1}{{11}} + ( - 1) = \frac{{ - 10}}{{11}}\];

c) \(\sqrt {\frac{9}{{64}}} :\frac{5}{4} + \sqrt {\frac{9}{{64}}} \,:\frac{5}{6} = \frac{3}{8}\,\,.\,\,\frac{4}{5} + \frac{3}{8}\,\,.\,\,\frac{6}{5} = \frac{3}{8}\,\,.\,\,\left( {\frac{4}{5} + \,\frac{6}{5}} \right) = \frac{3}{8}\,\,.\,\,2 = \frac{3}{4}\).