Ответ:

  1. \(10-5.9=4.1\); \(4.1+0.4=4.5\); \(4.5\cdot0.2=0.9\).
  2. \(0.4\cdot0.8=0.32\); \(0.32+0.48=0.8\); \(0.8-0.21=0.59\).
  3. \(7.9+1.1=9\); \(9\cdot0.7=6.3\); \(6.3-5.4=0.9\).
  4. \(120+90=210\); \(210\cdot0.02=4.2\); \(4.2-2.7=1.5\).

Ответ: 1) 0,9; 2) 0,59; 3) 0,9; 4) 1,5.