13. Вычислите: \(\frac{9}{10} + \frac{4}{9} \left( 2 - \frac{11}{21} \right) - \frac{1}{3}\). Запишите полностью решение и ответ.

Рассчитаем: \(\frac{9}{10} + \frac{4}{9} \left\(2 - \frac{11}{21} \right\) - \(\frac{1}{3}\) = \(\frac{9}{10}\) + \(\frac{4}{9}\) \(\cdot\) \(\frac{31}{21}\) - \(\frac{1}{3}\) = \(\frac{9}{10}\) + \(\frac{124}{189}\) - \(\frac{1}{3}\) = \(\frac{287}{315}\) + \(\frac{124}{189}\) - \(\frac{105}{315}\) = \(\frac{842}{945}\) = \(\frac{842}{945}\) = \(\frac{2}{3}\).