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1、乘法分配律,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,乘法交换律：,乘法结合律：,a b=b a,（ab）c=a（bc）,温故而知新,算一算,（3+2）4,34+24,（11+9）2,112+92,（20+4）
2、5,205+45,计算后仔细观察，说一说你发现了什么？,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,一共有25个小组，每组里4人负责挖坑、种树，2人负责抬水、浇树。,一共有多少名同学参加了这次植树活动？,说一说你
3、是怎样想的。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,我先求每组有多少人，再求参加植树活动的总人数。,（4+2）25625150（名）,答：一共有 150 名同学参加了这次植树活动。,我先求挖坑、种树的人数，
4、再求抬水、浇树的人数。,425+225100+50150（名）,答：一共有 150 名同学参加了这次植树活动。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,说一说,1.这两种做法有什么相同点和不同点？,2.你还能
5、举出像这样的等式吗？,（4+2）25 4 25+2 25,（3+2）4 3 4+2 4,（11+9）2 11 2+9 2,观察这些算式，说一说有什么特点？,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,（4+2）2
6、5 4 25+2 25,这叫做乘法分配律。,两个数的和与一个数相乘，可以先把它们与这个数分别相乘，再相加。,归纳讨论,用字母表示是：,（a+b）c,a c,+,b c,a（b+c）_,a b+a c,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元
7、成才路,状元成才路,状元成才路,填一填,1.（12+40）3=3+32.15（40+8）=15+15 3.7820+7822=（+）78,12,40,40,8,20,22,乘法分配律可以正着用，也可以反着用！,ac+bc=（a+b）c,1.下面哪些算式是正确的？正确的画“”，错误的画“”。56（19+28）=5619+28（）32（73）=327+323（）6464+3664=（64+36）64（）,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元
8、成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,乘法分配律,2.,巩固练习,1.判断正误：56（19+28）=5619+28（25+7）4=254+7432（73）=327+3236464+3664+1064=（64+36+10）64,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才
9、路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,2.连一连：,3 17+5 17,（184）6,22 30+44 30,60（20+30）,（22+44）30,18 64 6,60 20+60 30,（3+5）17,3.用乘法分配律计算下列各题,4715+5315 42101 6320163 12399,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状
10、元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,4.冷饮店运来 10 箱汽水和 20 箱橘子水，汽水和橘子水每箱都是 24 瓶。两种饮料一共多少瓶？（用两种方法解答）,1024+2024=720（瓶）（10+20）24=720（瓶）答：两种饮料一共720瓶。,课堂小结,通过本节的学习，说一说你有哪些认识和收获?,课后作业,1.课本 P28，第 7 题；2.完成练习册本课时的习题。,
