1、如在计算14+5时,先把14分成10和4,然后4和5先加等于9,然后再和前边的10相加等于19;2、 “借十法”(破十法):1.“借十法”是用在20以内退位减法中的计算方法.运用“借十法”可将20以内的退位减法转化为学生所熟悉的10减几的题目,从而化难为简.那么“借十法”在具体计算中是如何“凑”十的呢,我们看以下例题:在计算13减4时,先考虑个位3减4,不够减,于是从十位借10来减,10减4得6,再用6与个位数3相加等于9;这就是“借十法”.2.“借十法”口诀:借十法,很简单;十几减9,几加1;十几减8,几加2;十几减1,几加9. 3.根据口诀与例题掌握“借十法”. 凑 十 歌 一九一九好朋友
2、, 二八二八手拉手, 三七三七真亲密, 四六四六一起走. 五五凑成一双手. 一加九,十只小蝌蚪, 二加八,十只花老鸭, 三加七,十只老母鸡, 四加六,十只金丝猴, 五加五,十只大老虎. 看到9想到1, 看到8想到2, 看到7想到3, 看到6想到4. 看到大数加小数,. 一五6,二四6,三三6,四二6,五一6;6的组成没遗漏. 一六7,二五7,三四7,四三7,五二7,六一7;7的组成记仔细.一七8,二六8,三五8,四四8,五三8,六二8,七一8;8的组成记全它. 一八9,二七9,三六9,四五9,五四9,六三9,七二9,八一9; 9的组成全都有. 一九10,二八10,三七10,四六10,五五10,
3、六四10,七三10,八二10,九一10;10的组成共九句.【 练 习 题. 一 】 (凑 十 法)9 + 6 = 9 + 5 = 9 + 4 = 9 + 3 = 9 + 2 = 9 + 7 =9 + 8 = 9 + 9 = 8 + 8 =8 + 7 = 8 + 9 = 8 + 6 =8 + 5 = 8 + 4 = 8 + 3 =7 + 9 = 7 + 8 = 7 + 7 =7 + 6 = 7 + 4 = 7 + 5 =6 + 9 = 6 + 8 = 6 + 7 =6 + 6 = 6 + 5 = 5 + 9 =5 + 8 = 5 + 7 = 5 + 6 =4 + 9 = 4 + 8 = 4 +
4、7 =3 + 9 = 3 + 8 = 2 + 9 =【 练 习 题. 二 】 (破十法)18 9 = 17 9 = 16 9 = 15 9 = 11 4=14 9 = 13 9 = 12 9 = 11 9 = 12 3 =17 8 = 16 8 = 15 8 = 14 8 = 11 3 =13 8 = 12 8 = 11 8 = 16 7 = 11 2 =15 7 = 14 7 = 13 7 = 12 7 = 11 5 =11 7 = 15 6 = 14 6 = 13 6 = 12 4=12 6 = 11 6 = 14 5 = 13 5 = 13 4=【 练 习 题. 三 】 (20以内退位减
5、法)破十法口诀:看大数,分出10;减小数,加剩数.15 6 = 12 5 = 17 9 =13 4 = 11 5 = 14 7 =16 8 = 15 9 = 18 9 =12 7 = 14 9 = 13 7 = 12 9 = 11 3 = 12 4 =16 9 = 15 8 = 13 8 =11 6 = 13 4 = 14 5 =13 9 = 17 8 = 14 6=【 练 习 题. 四 】 (凑十法)1. 拆小数,凑大数9 + 9 = 9 + 8 = 9 + 7 =9 + 6 = 9 + 5 = 9 + 4 =9 + 3 = 9 + 2 = 8 + 8 =8 + 7 = 8 + 6 = 8
6、+ 5 =8 + 4 = 8 + 3 = 7 + 7 =7 + 6 = 7 + 5 = 7 + 4 =6 + 6 = 6 + 5 = 【 练 习 题. 五 】 (凑十法)2. 拆大数,凑小数9 + 9 = 8 + 9 = 7 + 9 =6 + 9 = 5 + 9 = 4 + 9 =3 + 9 = 2 + 9 = 8 + 8 =7 + 8 = 6 + 8 = 5 + 8 =4 + 8 = 3 + 8 = 7 + 7 =6 + 7 = 5 + 7 = 4 + 7 =6 + 6 = 5 + 6 = 【 练 习 题. 六 】 (凑十法)9 + 5 =9 + 7 =7 + 4 =8 + 5 =5 + 9
7、 =7 + 7 =5 + 8 =7 + 6 =6 + 8 =7 + 5 =5 + 7 =6 + 6 =6 + 9 =6 + 5 =5 + 6 =【 练 习 题. 七 】 (凑十法)8 + 6 =8 + 7 =6 + 7 =7 + 8 =4 + 7 =7 + 9 =9 + 4 =【 练 习 题. 八 】 (凑十法)15 - 6 = 14 - 5 = 13 - 4 =12 - 3 = 11 - 2 = 16 - 7 =17 - 8 = 18 - 9 = 16 - 8 =15 - 7 = 17 - 9 = 14 - 6 =13 - 5 = 12 - 4 = 11 - 3 =16 - 9 = 15 -
8、 8 = 14 - 7 =13 - 6 = 11 - 4 = 12 - 5 =15 - 9 = 14 - 8 = 13 - 7 =12 - 6 = 11 - 5 = 14 - 9 =13 - 8 = 12 - 7 = 11 - 6 =13 - 9 = 12 - 8 = 11 - 7 =12 - 9 = 11 - 8 = 11 - 9 =【 练 习 题. 九 】 (凑十法)1. 拆小数,凑大数,凑成10,再相加 .9 + 8 = 9 + 7 = 9 + 6 =9 + 5 = 9 + 4 = 9 + 3 =9 + 2 = 8 + 7 = 8 + 6 =6 + 5 = 【 练 习 题. 十 】 (凑
9、十法)2. 拆大数,凑小数,凑成10,再相加 .8 + 9 = 7 + 9 = 6 + 9 =5 + 9 = 4 + 9 = 3 + 9 =2 + 9 = 7 + 8 = 6 + 8 =5 + 8 = 4 + 8 = 3 + 8 =5 + 6 = 3.9 + 9 = 8 + 8 = 7 + 7 = 6 + 6 = 【 练 习 题. 十一 】 (凑十法)【 练 习 题. 十二 】 (凑十法) 【 练 习 题. 十三 】 (凑十法)一、用凑十法做一做.9 + 6 = 9 + 5 = 9 + 4 = 9 + 3 = 9 + 2 = 9 + 7 = 9 + 8 = 9 + 9 =8 + 8 = 8 +
10、 7 = 8 + 9 = 8 + 6 =8 + 5 = 8 + 4 = 8 + 3 = 7 + 9 =7 + 8 = 7 + 7 = 7 + 6 = 7 + 4 =7 + 5 = 6 + 9 = 6 + 8 = 6 + 7 =6 + 6 = 6 + 5 = 5 + 9 = 5 + 8 =5 + 7 = 5 + 6 = 4 + 9 = 4 + 8 =4 + 7 = 3 + 9 = 3 + 8 = 2 + 9 =【 练 习 题. 十四 】 (20以内退位减)15 6 = 12 5 = 17 9 = 13 4 = 11 5 = 14 7 = 16 8 = 15 9 =18 9 = 12 7 = 14
11、 9 = 13 7 =12 9 = 11 3 = 12 4 = 16 9 =15 8 = 13 8 = 11 6 = 13 4 = 14 5 = 13 9 = 17 8 = 14 6=【 练 习 题. 十五 】 (20以内退位减)15 - 6 =20以内减法:14 - 6 =17 - 9 =16 - 8 =11- 8 =12 - 7 =12 - 5 =13- 7 =13 - 8 =14 - 9 =15- 7 =13 - 5 =18 - 9 =11 - 7 =17- 8 =19 - 7 =【 练 习 题. 十六 】 (20以内退位减)【练 习 题. 十七 】 (凑十法)二、填出括号里的数.8+(
12、 )=10 10+( )=14 6+( )=15( )+4=13 ( )+6=13 ( )+7=116+( )=14 ( )+9=12 8+( )=13三、填空.1、最小的一位数是( ),最大的一位数是( ),最小的两位数是( ).2、从右边起,第一位是( )位,第二位是( )位.有个十在十位写( ),有个十在十位写( ),有几个一在个位写( ).个位上的数是几就表示几个( ),十位上的数是几就表示几个( ).3、20以内数中的双数是:4、20以内数中的单数是:【练 习 题. 十八 】 (凑十法,破十法)9 + 2 = 9 + 7 = 9 + 8 = 9 + 9 =15 6 = 12 5 =
13、17 9 = 13 4 =14 5 = 13 9 = 17 8 = 14 6=【练 习 题. 十九 】 (20以内退位减法)【练 习 题. 二十 】 (20以内退位减法)20以内退位减法破十法、凑十法复习【重点知识一】凑十法:进位加法使用凑十法口诀:看大数,分小数,凑成十,算得数例子:巩固练习:【重点知识二】破十法:退位减法使用看大数,分出10,减小数,加剩数18 9 = 17 9 = 16 9 = 15 9 =17 8 = 16 8 = 15 8 = 14 8 =13 8 = 12 8 = 11 8 = 16 7 = 【练 习 题. 二十一 】提升练习题一、 口算12 6 = 11 6 =
14、14 5 = 13 5 = 3 + 9 = 7 + 8 = 9 + 7 =二、 判断里的数对不对?对的画“”,错的画“”.( )( )( )( )( )( )三、填空115比( )多3. 2 ( )比12少5.3 ( )比20少5. 417比( )少3.5 ( )比19多1. 6 ( )比12多4.四、看图列式五、应用题1小雨和小雪共画了15朵花,小雨画了9朵,小雪画了几朵?2小明有18枝彩色笔,小刚借走了9枝,小明还有几枝?3同学们排队,小兰的前边有5人,后面有7人,这一行共有多少人?4同学们排队,小兰的前边有5人,后面有7人,这一行共有多少人?5停车场上的汽车开走了6辆,又开走了5辆,一共开走了多少辆?
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