Thực hiện phép tính (tính hợp lí nếu có thể): n) − 4/12 + 18 /45 + − 6/9 + − 21/35 + 6/30 .

n) −412+1845+−69+−2135+630.

n) \(\frac{{ - 4}}{{12}} + \frac{{18}}{{45}} + \frac{{ - 6}}{9} + \frac{{ - 21}}{{35}} + \frac{6}{{30}}\)

\( = \frac{{ - 1}}{3} + \frac{2}{5} + \frac{{ - 2}}{3} + \frac{{ - 3}}{5} + \frac{1}{5}\)\( = \left( {\frac{{ - 1}}{3} + \frac{{ - 2}}{3}} \right) + \left( {\frac{2}{5} + \frac{{ - 3}}{5} + \frac{1}{5}} \right)\)

\( = \frac{{ - 3}}{3} + \frac{0}{5} = - 1.\)