Tính bằng cách thuận tiện nhất: 1/15 + 4/15 + 5/18 + 7/18

\[\frac{1}{{15}} + \frac{4}{{15}} + \frac{5}{{18}} + \frac{7}{{18}}\]

\[ = \left( {\frac{1}{{15}} + \frac{4}{{15}}} \right) + \left( {\frac{5}{{18}} + \frac{7}{{18}}} \right)\]

\[ = \frac{5}{{15}} + \frac{{12}}{{18}}\]

\[ = \frac{1}{3} + \frac{2}{3}\]

\[ = \frac{3}{3} = 1\]