Thực hiện phép tính (tính hợp lí nếu có thể):     a) 0,25 - 1,25.9;  b) - 7/16+ 3/4

a) \(0,25 - 1,25.9\)

\( = 0,25 - 11,25\)

\( =  - 11\).

b) \(\frac{{ - 7}}{{16}} + \frac{3}{4}\)

\( = \frac{{ - 7}}{{16}} + \frac{{12}}{{16}}\)

\( = \frac{5}{{16}}\).

c) \( - 3,5 + 4,6 + 3,5 + \left( { - 1,6} \right)\)

\( = \left( { - 3,5 + 3,5} \right) + \left[ {4,6 + \left( { - 1,6} \right)} \right]\)

\( = 0 + 3 = 3\).

d) \(\frac{4}{9}.\frac{{ - 7}}{{26}} + \frac{{45}}{{ - 26}}.\frac{4}{9} + \frac{1}{3}\)

\( = \frac{4}{9}.\frac{{ - 7}}{{26}} - \frac{{45}}{{26}}.\frac{4}{9} + \frac{1}{3}\)

\( = \frac{4}{9}.\left( {\frac{{ - 7}}{{26}} - \frac{{45}}{{26}}} \right) + \frac{1}{3}\)

\( = \frac{4}{9}.\frac{{ - 52}}{{26}} + \frac{1}{3}\)

\( = \frac{4}{9}.\left( { - 2} \right) + \frac{1}{3}\)

\( = \frac{{ - 8}}{9} + \frac{3}{9} = \frac{{ - 5}}{9}\).