Thực hiện phép tính (tính hợp lí nếu có thể): a) - 2,13  - (- 3,37);  b) 2/5 - 1/5.3/- 4

a) \[ - 2,13  - \left( { - 3,37} \right)\]

\[ =  - 2,13 + 3,37\]

\[ = 1,24\].

c) \(0,25.\frac{7}{{15}} - 25\% .\frac{{ - 8}}{{15}} + 2,75\)

\[ = 0,25.\frac{7}{{15}} + 0,25.\frac{8}{{15}} + 2,75\]

\[ = 0,25.\left( {\frac{7}{{15}} + \frac{8}{{15}}} \right) + 2,75\]

\[ = 0,25.\frac{{15}}{{15}} + 2,75\]

\[ = 0,25 + 2,75 = 3\].

b) \(\frac{2}{5} - \frac{1}{5}.\frac{3}{{ - 4}}\)

\( = \frac{2}{5} + \frac{3}{{20}}\)

\( = \frac{8}{{20}} + \frac{3}{{20}} = \frac{{11}}{{20}}\).

d) \(\frac{3}{4}.26\frac{2}{9} - 38\frac{2}{9}.\frac{3}{4}\)

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

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

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