第2课时乘、除法的意义和各部分间的关系四则运算1优翼www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com5+5+5=12+12+12+12+12=1560复习导入一 www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com（1）每个花瓶里插3枝花，4个花瓶一共插了多少枝花？用加法：3+3+3+3＝12用乘法：3×4＝12。求几个相同加数的和的简便运算，叫做乘法。2探索新知二 www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com乘法算式各部分名称：3×4＝12因数因数积探索新知二 www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com（2）有12枝花，每3枝插一瓶，可以插几瓶？（3）有12枝花，平均插到4个花瓶里，每个花瓶插几枝？12÷3=412÷4=3探索新知二 www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com想一想：与第（1）相比，第（2）、（3）题分别是已知什么？求什么？怎样算？探索新知二 www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com除法是已知两个因数的积与其中一个因数，求另一个因数的运算。除法是乘法的逆运算。明确除法的意义探索新知二在除法中，已知的积叫做被除数。 www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com一起总结一下乘、除法各部分间的关系。积=因数×因数因数=积÷另一个因数1.乘法各部分间的关系探索新知二 www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com商=被除数÷除数除数=被除数÷商被除数=商×除数2.除法各部分间的关系探索新知二 www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com想一想：在有余数的除法里，被除数与商、除数和余数之间有什么关系？例：19÷6＝3……1被除数＝商×除数＋余数探索新知二 www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com问题：你是根据什么得出结果的？3614根据36×14＝504，直接写出下面两道题的得数。504÷14＝504÷36＝巩固练习三 www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com1.四年级有4个班，每班40人，一共有多少人？40×4=160（人）2.四年级有160人，平均分成4个班，每班多少人？160÷4=40（人）3.四年级有160人，每40人分一班，可分成几个班？160÷40=4（个）巩固练习三 www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com4.水果店运来20筐苹果，共500千克。平均每筐苹果有多少千克？500÷20=255.光明小学有2400本图书。图书的本数正好是学生人数的4倍。光明小学有多少名学生？2400÷4=600巩固练习三 www.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.comwww.youyi100.com积=因数×因数因数=积÷另一个因数商=被除数÷除数除数=被除数÷商被除数=商×除数课堂小结四