2.4x2.1x20.3=2.4x(2+0.1)x(20+0.3)=(4.8+0.24)x(20+0.3)=5.04x(20+0.3)=5.04x20+5.04x0.3=100.8+1.512=102.312
2.4*2.1+20.3=5.04+20.3=25.34满意采纳奥