1. Выполните вычисления: а) \( (1\frac{1}{9}-5\frac{1}{3}):(-\frac{1}{5}+2,1) \); б) \( 4-(4\frac{21}{40}-5,25):1\frac{9}{20} \).

а)

\(1\frac{1}{9}=\frac{10}{9},\quad 5\frac{1}{3}=\frac{16}{3},\quad 2,1=\frac{21}{10}\).

\[\left(\frac{10}{9}-\frac{16}{3}\right):\left(-\frac{1}{5}+\frac{21}{10}\right)=\left(-\frac{38}{9}\right):\frac{19}{10}= -\frac{38}{9}\cdot\frac{10}{19}=-\frac{20}{9}.\]

б)

\(4\frac{21}{40}=\frac{181}{40},\quad 5,25=\frac{21}{4},\quad 1\frac{9}{20}=\frac{29}{20}\).

\[4-\left(\frac{181}{40}-\frac{210}{40}\right):\frac{29}{20}=4-\left(-\frac{29}{40}\right)\cdot\frac{20}{29}=4+\frac{1}{2}=4,5.\]

Ответ: а) \(-\frac{20}{9}\); б) \(4,5\).