Thực hiện phép tính (tính hợp lí nếu có thể): a) 14,9 +(- 8,3) + (- 4,9); b) 7/4- 3/4:- 1/3

a) \(14,9 + \left( { - 8,3} \right) + \left( { - 4,9} \right)\)

\[ = \left[ {14,9 + \left( { - 4,9} \right)} \right] + \left( { - 8,3} \right)\]

\[ = 10 - 8,3\]

\[ = 1,7\].

c) \[\frac{{ - 1}}{4}.\left( {12\frac{3}{4} - 7,75} \right) - 25\% .3\frac{1}{2}\]

\[ = \frac{{ - 1}}{4}.\left( {12,75 - 7,75} \right) - \frac{{25}}{{100}}.\frac{7}{2}\]

\[ = \frac{{ - 1}}{4}.5 - \frac{1}{4}.\frac{7}{2}\]

\[ = \frac{{ - 5}}{4} - \frac{7}{8}\]

\[ = \frac{{ - 10}}{8} - \frac{7}{8}\]

\[ = \frac{{ - 17}}{8}\].

b) \(\frac{7}{4} - \frac{3}{4}:\frac{{ - 1}}{3}\)

\( = \frac{7}{4} - \frac{3}{4}.\left( { - 3} \right)\)

\( = \frac{7}{4} + \frac{9}{4}\)

\( = \frac{{16}}{4} = 4\).

d) \(\frac{{ - 5}}{{17}}.\frac{{31}}{{33}} - \frac{5}{{17}}.\frac{2}{{33}} + 1\frac{5}{{17}}\)

\( = \frac{{ - 5}}{{17}}.\left( {\frac{{31}}{{33}} + \frac{2}{{33}}} \right) + \frac{{22}}{{17}}\)

\( = \frac{{ - 5}}{{17}}.1 + \frac{{22}}{{17}}\)

\( = \frac{{17}}{{17}} = 1\).