Thực hiện phép tính dưới đây: (a) ( − 6 , 4 ) + ( − 8 , 3 ) + 6 , 4 − 1 , 7 . (b) 7/15 .1 14/33 + 19/33 : 15/7 − 7/15 .

a) \[\left( { - 6,4} \right) + \left( { - 8,3} \right) + 6,4 - 1,7\]

\[ = \left[ {\left( { - 6,4} \right) + 6,4} \right] + \left( { - 8,3 - 1,7} \right)\]

\[ = 0 + \left( { - 10} \right)\]\[ = - 10\].

b) \(\frac{7}{{15}}.1\frac{{14}}{{33}} + \frac{{19}}{{33}}:\frac{{15}}{7} - \frac{7}{{15}}\)

\( = \frac{7}{{15}}.1\frac{{14}}{{33}} + \frac{{19}}{{33}}.\frac{7}{{15}} - \frac{7}{{15}}.1\)

\( = \frac{7}{{15}}.\left( {1\frac{{14}}{{33}} + \frac{{19}}{{33}} - 1} \right)\)

\( = \frac{7}{{15}}.1\)\( = \frac{7}{{15}}\).

c) \(\frac{1}{2} + \frac{{35}}{{78}} - 1\frac{5}{{37}} - \left( {1\frac{{35}}{{78}} + \frac{{32}}{{37}} - 2,5} \right)\)

\( = \frac{1}{2} + \frac{{35}}{{78}} - 1\frac{5}{{37}} - 1\frac{{35}}{{78}} - \frac{{32}}{{37}} + 2,5\)

\( = \left( {\frac{1}{2} + \frac{5}{2}} \right) + \left( {\frac{{35}}{{78}} - 1\frac{{35}}{{78}}} \right) - \left( {1\frac{5}{{37}} + \frac{{32}}{{37}}} \right)\)

\( = 3 + \left( { - 1} \right) - 2\)

\( = 0\).