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荣德基,荣德基,荣德基,荣德基,荣德基,荣德基,荣德基,荣德基,荣德基,荣德基,第,4,课时 十几减5、4、3、2,RJ,一年级下册,2 20以内的退位减法,1.,口算。,15,6=,12,7=,11,6=,13,9=,14,8=,17,9=,15,7=,14,7=,9,5,6,8,5,4,8,7,2.,填一填。,9,( ),=12,6,( ),=11,8,( ),=12,7,( ),=12,7,( ),=11,9,( ),=11,3,5,4,5,4,2,12,5=,11,4=,12,4=,11,3=,12,3=,11,2=,7,8,9,7,8,9,4,探究点,十几减,5,、,4,、,3,、,2,的计算方法,你是怎么算的?,2,10,5,7,7,12,5 ,7 + 5 12,12,5 7,破十法,想加算,减法,平十法,12,2,10,10,3,7,12,5 ,2,3,10,7,7,12,5=,11,4=,12,4=,11,3=,12,3=,11,2=,7,8,9,7,8,9,下面两列算式有什么特点?,竖着观察,左右两列的被减数不变,减数逐渐少“,1,”,差逐渐多“,1,” ;横着观察,每一行被减数相差“,1,”,减数也相差“,1,”,差不变。,5,=13,8,13,5=,4,=13,13,4=,5,=14,14,5=,5,=11,11,5=,8,9,9,9,9,6,6,11,5,12,5,14,6,12,2,16,4,13,7,13,6,15,7,15,5,18,6,14,8,17,9,19,9,19,7,15,9,找出得数相同的卡片来。,得数是,6,:,12,5,14,6,12,2,16,4,13,6,15,7,15,5,18,6,17,9,19,9,19,7,找出得数相同的卡片来。,得数是,7,:,14,6,12,2,16,4,15,7,15,5,18,6,17,9,19,9,19,7,找出得数相同的卡片来。,得数是,8,:,12,2,16,4,15,5,18,6,19,9,19,7,找出得数相同的卡片来。,得数是,10,:,16,4,18,6,19,7,找出得数相同的卡片来。,得数是,12,:,得数是,6,:,11,5,得数是,7,:,12,5,得数是,8,:,14,6,得数是,10,:,12,2,得数是,12,:,16,4,13,7,13,6,15,7,15,5,18,6,14,8,17,9,19,9,19,7,15,9,你发现了什么?,两个算式中,两个被减数相差,1,,减数也相差,1,,差相等。,思考题,用,19,这九个数填一填。你能组成多少组这样的算式(每个算式只有,1,可以重复使用)?,=,=,=,1 5 6 1 7 8,1,4,7,1,5,8,1,3,8,1,4,9,1.,小动物喜欢吃什么?,4,8,6,11,3,3,15,7,6,5,4,7,8,7,9,19,5,8,12,4,5,17,2,4,18,5,14,16,6,6,13,19,2.,3.,下面每组算式卡片的得数相同,你能填出被遮住的数吗?,4,7,2,14,4,4,(,1,)一共摘了,13,个桃子。吃了,9,个,还剩几个?,(,2,)一共有,13,只猴子。树上有 只,树下有几只?, (个),(只),13,9,4,13,4,9,4,4.,5.,算一算,练一练。,小兔可以选哪,两棵白菜,?,14,9,5 13,8,512,7,5,十几减,5,、,4,、,3,、,2,的计算方法:,十几减,5,、,4,、,3,、,2,的计算方法与十几减,9,、,8,、,7,、,6,的计算方法相同,可以用“,破十法,”“,想加算减法,”“,平十法,”等方法进行计算。,
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