Решение:
$$(\frac{11}{12} - \frac{3}{15}) + (\frac{7}{20} - \frac{1}{30}) - \frac{2}{3} = (\frac{55}{60} - \frac{12}{60}) + (\frac{21}{60} - \frac{2}{60}) - \frac{2}{3} = \frac{43}{60} + \frac{19}{60} - \frac{2}{3} = \frac{62}{60} - \frac{40}{60} = \frac{22}{60} = \frac{11}{30}$$
Ответ: \(\frac{11}{30}\)