12.5x4x8x2.5=(12.5x8)x(4x2.5)=100x10=1000
1.25x7.7+2.3x1.25=1.25x(7.7+2.3)=1.25x10=12.5
100-123.1x0.3=100+100x0.3+23.1x0.3=100x1.3+23.1x0.3=130+6.93=136.93
2.14+0.39除以1.3=2.14+(39/13)/10=2.14+3/10=2.44
1.25x70.7+1.25x2.3=1.25x(70.7+2.3)=1.25x73=91.25
2.1x5.5=2.1x(5+0.5)=2.1x5+2.1x0.5=10.5+1.05=11.55