1.2×5.2一2.5÷0.3=1.2x（5+0.2)-(2.4+0.1)÷0.3=1.2x5+1.2x0.2-2.4÷0.3-0.1÷0.3=0.3x4x5+0.24-8-1/3=0.3x20+0.24-8-1/3=6+0.24-8-1/3=-2+0.24-1/3≈-2+0.24-0.34=-2-0.1=-2.1
