1) (-0,251+0,37)+(-0,2+(-0,152)) = 0.119+(-0.2-0.152) = 0.119+(-0.352) = 0.119-0.352 = -0.233
2) (- 3 3/8+4 1/4)+(-1 5/6+(-2 5/12)) = (-27/8+17/4)+(-11/6-2 5/12) = (-27+34)/8+(-11/6-29/12) = 7/8+(-(22+29)/12) = 7/8+(-51/12) = 7/8 - 57/12 = 7/8-17/4 = (7-34)/8 = -27/8 = -3.375
3) (-2/3+(-2/15))+(-1,85+(-1,35)) = (-2/3-2/15)+(-1.85-1.35) = (-(10+2)/15)+(-3.2) = (-12/15)-3.2 = -12/15-3.2 = -4/5-3.2 = -0.8-3.2 = -4