Вариант 4. Вычислите: 1) 0.6 + 3/8; 2) 7/20 − 0.35; 3) −7.4 − 1/2; 4) −2 − (−0.86); 5) 4 1/2 − (−0.25); 6) −4.2 · 3/7; 7) −0.8 · (−3/50); 8) −20 : (−1/5); 9) −1 4/9 : 18; 10) −3.5 : (−0.05).

1. \(0.6+\frac{3}{8}=\frac{3}{5}+\frac{3}{8}=\frac{24+15}{40}=\frac{39}{40}\).
2. \(\frac{7}{20}-0.35=0.35-0.35=0\).
3. \(-7.4-\frac{1}{2}=-7.4-0.5=-7.9\).
4. \(-2-(-0.86)=-2+0.86=-1.14\).
5. \(4\frac{1}{2}-(-0.25)=4.5+0.25=4.75\).
6. \(-4.2\cdot\frac{3}{7}=-1.8\).
7. \(-0.8\cdot\left(-\frac{3}{50}\right)=0.8\cdot0.06=0.048\).
8. \(-20:\left(-\frac{1}{5}\right)=(-20)\cdot(-5)=100\).
9. \(-1\frac{4}{9}:18=-\frac{13}{9}:18=-\frac{13}{9}\cdot\frac{1}{18}=-\frac{13}{162}\).
10. \(-3.5:(-0.05)=70\).

Ответ: 1) \(\frac{39}{40}\); 2) 0; 3) −7.9; 4) −1.14; 5) 4.75; 6) −1.8; 7) 0.048; 8) 100; 9) \(−\frac{13}{162}\); 10) 70.