Tính. (1 điểm)

a) \(\frac{7}{{12}} + \frac{4}{{15}} = \frac{{7 \times 5}}{{12 \times 5}} + \frac{{4 \times 4}}{{15 \times 4}}\, = \frac{{35}}{{60}} + \frac{{16}}{{60}}\, = \frac{{51}}{{60}}\)

b) \(\frac{5}{8} - \frac{{11}}{{18}} = \frac{{5 \times 9}}{{8 \times 9}} - \frac{{11 \times 4}}{{18 \times 4}} = \frac{{45}}{{72}} - \frac{{44}}{{72}}\, = \frac{1}{{72}}\)

c) \(\frac{7}{{11}} \times \frac{{44}}{{21}} = \frac{7}{{11}} \times \frac{{4 \times 11}}{{7 \times 3}} = \frac{{\cancel{7} \times 4 \times \cancel{{11}}}}{{\cancel{{11}} \times \cancel{7} \times 3}} = \frac{4}{3}\)

d) \(\frac{4}{{27}}:\frac{2}{3} = \frac{4}{{27}} \times \frac{3}{2} = \frac{{2 \times 2}}{{9 \times 3}} \times \frac{3}{2} = \frac{{\cancel{2} \times 2 \times \cancel{3}}}{{9 \times \cancel{3} \times \cancel{2}}} = \frac{2}{9}\)