4.7×2.9 +42×0.29 +130×0.029=2.9x(4.7+4.2+1.3)=2.9x(10+0.2)=29+5.8=34.8
4.7×2.9 42×0.29 130×0.029简便计算=2.9x（4.7+4.2+1.3）=2.9x10.2=2.9x10+2.9x0.2=29+0.58=29.58
