Ответ:

  1. \(3.4+4.3-6.9\cdot5=7.7-34.5=-26.8\).
  2. \(3\cdot1.3+0.1-2.2=3.9+0.1-2.2=1.8\).
  3. \(6.3-5.8+0.3\cdot7=0.5+2.1=2.6\).
  4. \(2.6+0.7-1.8\cdot5=3.3-9=-5.7\).

Ответ: 1) −26,8; 2) 1,8; 3) 2,6; 4) −5,7.