Tính rồi rút gọn.

\[\frac{{11}}{{18}} + \frac{7}{{18}} = \frac{{11 + 7}}{{18}} = \frac{{18}}{{18}} = 1\]

\[\frac{{21}}{{22}} - \frac{5}{{22}} = \frac{{21 - 5}}{{22}} = \frac{{16}}{{22}} = \frac{{16:2}}{{22:2}} = \frac{8}{{11}}\]

\[\frac{7}{{20}} + \frac{9}{{20}} = \frac{{7 + 9}}{{20}} = \frac{{15}}{{20}} = \frac{{15:5}}{{20:5}} = \frac{3}{4}\]

\[\frac{{41}}{{35}} - \frac{{16}}{{35}} = \frac{{41 - 16}}{{35}} = \frac{{25}}{{35}} = \frac{{25:5}}{{35:5}} = \frac{5}{7}\]