Ответ:\(1-\frac a5-\frac b4=\frac{20-4a-5b}{20}\).\(12-1-\frac1b=11-\frac1b=\frac{11b-1}{b}\).\(\frac{a-2}{2}-1-\frac{a-3}{3}=\frac{3a-6-6-2a+6}{6}=\frac{a-6}{6}\).\(4a-\frac14-a+\frac23=3a+\frac5{12}=\frac{36a+5}{12}\).