а) 0,12 − 1,375; б) 1 2/3 − (−0,75); в) −4,2 − 3,25 − (−1/12); г) 4 8/15 − 6 7/12 − (−5 3/40).

1. \(0.12-1.375=-1.255\).
2. \(1\frac{2}{3}-(-0.75)=\frac{5}{3}+\frac{3}{4}=\frac{20}{12}+\frac{9}{12}=\frac{29}{12}=2\frac{5}{12}\).
3. \(-4.2-3.25-\left(-\frac{1}{12}\right)=-7.45+\frac{1}{12}=-\frac{149}{20}+\frac{1}{12}=-\frac{447}{60}+\frac{5}{60}=-\frac{442}{60}=-\frac{221}{30}=-7\frac{11}{30}\).
4. \(4\frac{8}{15}-6\frac{7}{12}-\left(-5\frac{3}{40}\right)=\frac{68}{15}-\frac{79}{12}+\frac{203}{40}\). Приведём к знаменателю \(120\): \(\frac{544}{120}-\frac{790}{120}+\frac{609}{120}=\frac{363}{120}=\frac{121}{40}=3\frac{1}{40}\).

Ответ: а) −1,255; б) 2 5/12; в) −7 11/30; г) 3 1/40.