第32课时 初商过小需调商的除法

教学内容：p54—55《作业本》p32                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             

教学目标：

1、    通过教学，使学生了解用五入试商时，有时会出现初商过小的情况，掌握初商过小时调商的方法。

2、    学生能熟练地计算。

3、    培养学生的估商能力，提高学生地计算能力。

教学重点：把除数“五入”看成接近的整十数去试商时，有时会产生初商过小的情况，需调商。

教学难点：调商的方法。

教学过程

一、引入

  1、（  ）里最大能填几？

     58×（  ）〈 350           49×（   ）〈 248

     37×（  ）〈154            68×（   ）〈 492

  2、计算  382÷48

（1）独立完成

（2）指明说说计算时怎样试商？

（3）如果把382改成392又是怎样计算呢？

二、引导探究

  1、出示  392÷48

（1）学生尝试计算，指名板演。

（2）小组交流：说说自己是怎样试商的？在计算时碰到什么问题？又是怎样解决问题的？

（3）全班交流：为什么商会过小？

（4）小结：“五入”后试商，由于除数变大，商容易过小，出现余数比除数大的情况，说明商小了，要把商调大。

  2、试一试

        276÷39        489÷68

  3、小结揭题 ：上面的几道题在计算中都有碰到什么情况？你能根据上面的特点，把几天学习的内容取一个题目吗？

          板书：“初商过小需调商的除法”

三、巩固练习

   1、在下面的○里填上〈、〉或=

49×3○149                62×7○415

58×6○358                97×4○388

   2、计算

       48）446            67）482           78）639

 39）318            28）250           57）537

   3、下面的计算对吗？把不对的改正过来？

                6               9                 8

    24）124         31）270           63）496

        144             279               447

         20               0                51

   4、文字题 p55 t3

四、课堂总结

今天这节课我们学习了什么内容？在计算的过程中要注意什么？

五、课堂作业

1、《作业本》p32

2、课本p55 t4、5

六、板书设计

初商过小需调商的除法

            例7  392÷48=8…8

            50    7                8

            48）392          48）392

                336              384

                 56

             商7小了           改商8