乘法分配律及简单应用.ppt

1、第 5 课时 乘法分配律,R四年级下册,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,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,（1

2、1+9）2,112+92,（20+4）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

3、少名同学参加了这次植树活动？,说一说你是怎样想的。,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）25 625 150（名）,答：一共有 150 名同学参加

4、了这次植树活动。,我先求挖坑、种树的人数，再求抬水、浇树的人数。,425+225 100+50 150（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

5、. 这两种做法有什么相同点和不同点？,2. 你还能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

6、,状元成才路,状元成才路,状元成才路,状元成才路,（4+2）25 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

7、路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,填一填,1.（12+40）3 = 3+ 3 2. 15（40+8）= 15 + 15 3. 7820+7822 =（ + ）78 4. 6628+6632+6640 =（ + + ）,12,40,40,8,20,22,28,32,40,66,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

8、）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,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,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+74 32（73）= 327+323 6

9、464+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,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,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

10、 + 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 6320163 （208）125 12399 42101,=1500,=12600,=1500,=12177,=4242,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,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