1.103*12
=(100+3)*12
=100*12+3*12
=1200+36
=1236
2.20*55
=20*(50+5)
=20*50+20*5
=1000+100
=1100
3.24*205
=24*(200+5)
=24*200+24*5
=4800+120
=4920
103*(10+2)=1030+206=1236,20*55=1100,24*205=(20+4)*205=4100+80=4180
103分成100和3,分别乘以12
103×12=(100+3)×12=1200+36=1236
20×55=20×(50+5)=1000+100=1100
24×205=24×(200+5)=4800+120=4920
(100+3)x12=100x12+3x12:20x(50+5)=20x50+20x5:24x(200+5)=24x2oo+24x5