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优翼www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com第1课时十几减920以内的退位减法2
一情境导入www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com问题:3.6+7得多少?你是怎么算的?2.图中一共有多少条金鱼?你是怎么知道的?1.在图中你都看到了什么?
优翼文化二探究新知www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com2.要求的问题是什么?(一)提取信息问题:11.从图中你都知道了什么?
优翼文化二探究新知www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com问题:14.这个6是怎么得到的啊?把你们的算法和同桌的小朋友说一说,也可以用学具摆一摆。3.你能列算式解决一下吗?15-9=6
www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com(二)解决问题反馈:1.数数问题:你能到前面,对着图边指边数吗?2.摆一摆优翼文化二探究新知
www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com3.想加算减9+()=1515-9=()4.平十法15-5=1010-4=6问题:(1)5和4哪来的?(2)为什么把9分成5和4?66优翼文化二探究新知
www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com5.破十法10-9=15+1=6问题:(1)这种算法谁能看懂?什么意思?(2)谁能用图把这种方法演示出来?优翼文化二探究新知
www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com问题:(2)10-9所得的1为什么还要和5相加?小结:15-9,个位的5不够减9,用10减9,10-9=1,1再加5等于6。(3)谁也是用这种方法算的?你能再说说吗?(1)为什么先用10减9?优翼文化二探究新知
三对应练习www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com问题:你能用你喜欢的方法算算这两道题吗?(反馈的重点放在想加算减和破十法上。)1.用摆一摆,算一算。27
三对应练习www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com2.圈一圈,算一算。问题:(1)结果是多少?(2)为什么这么圈?58
三对应练习www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com3.为什么后一道题的差比前一道题的差多“1”?2.仔细观察这些算式,你发现了什么?11-9=212-9=313-9=414-9=515-9=616-9=717-9=818-9=9问题:1.十几减9的题还有哪些?你能把它说出来并且直接计算出结果吗?
三对应练习www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com问题:(1)你从题中知道了什么?问题:(2)要求的问题是什么?问题:(3)你能试着解决这个问题吗?
三对应练习www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com16-9=?9-3=?谁剩的苹果多?16-9=79-3=6白狐狸剩的苹果多。>
四课堂小结1.通过比较发现:15-9的计算方法有画一画、圈一圈、点数法、破十法、平十法、想加算减法等,我们可以选择自己喜欢的方法来解题。2.总结计算十几减9的口诀:十几减9莫要急,“破十”计算是真理,分10减9还剩1,结果就是1加几。www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com
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