20以内的加减法: 进位:(1+19,2+18,....9+11),(9+9,9+8,9+7,...9+1),(8+8,8+7,...8+2),(7+7,7+6,....7+3),........5+5. 推位:20-19,20-18,...20-1),(18-9,17-9,17-8,16-9,16-8,16-7,.....,11-8,....11-2
20以内的加减法: 进位:(1+19,2+18,....9+11),(9+9,9+8,9+7,...9+1),(8+8,8+7,...8+2),(7+7,7+6,....7+3),........5+5. 推位:20-19,20-18,...20-1),(18-9,17-9,17-8,16-9,16-8,16-7,.....,11-8,....11-2