小学数学人教一年级两位数减一位数退位减.pptx

,R,一,年级下册,两位数减一位数（退位）,一、引入新课,回顾,57,4,57,40,75,3,75,30,69,5,69,50,53,17,72,45,64,19,二、探索新知,我借,8,个足球。,还剩下多少个足球？,36,8,二、探究新知,36,8,28,先算,36,6,30,再算,30,2,28,36,8,算法一,8,26,10,2,28,8,36,8,算法二,20,16,8,28,8,8,把,36,分成,20,和,18,先算,16-8=8,再算,20+8=28,7,6,4,5,7,3,6,4,3,7,6,8,5,7,9,6,4,8,7,2,5,4,6,1,6,8,4,8,5,6,不退位减法,退位减法,第二组都是个位不够减，要从十位上退,1,，是退位减法。,第一组都是个位够减，十位上的数没变，是不退位减法。,42 8=,第一关,。,30,12,4,34,第二关,1.,想一想，算一算。,（,1,）,47 8=,先算,再算,=,+=,17,（,2,）,36 9=,先算,再算,=,+=,8,9,30,9,39,39,16,9,7,20,7,27,27,第三关,做,1.,先圈一圈，再计算。,32 5=,=,+=,先算,再算,44 9=,=,+=,先算,再算,12,5,7,20,7,27,27,14,9,5,30,5,35,35,2.,30 6=_,20,10,想一想,0,减,6,不够减，先算什么？,再算什么？,先算,10 6=4,再算,20+4=24,24,四、课堂小结,两位数减一,位数（退位,）,36,8,20,16,8,28,26,10,2,36,8,28,五、课后作业,1.,从课后习题中选取；,2.,完成练习册本课时的习题。,