人教版小学数学五年级下册第五单元分数加减混合运算第一课时

1、课题： 分数加减混合运算(一) 教学目标1、通过教学，使学生掌握分数加减混合运算的顺序和计算方法，并掌握带有小括号的分数加减混合运算的顺序及算法。2、培养学生迁移、类推的能力和归纳、概括的能力。3、养成用简明、灵活的方法解决问题的习惯。重点难点掌握分数加减混合运算的顺序和计算方法。 教学过程 第一课时一、复习导入1 说一说下列各题的运算顺序。112+8-13 16-4+21 24-(18+3) 2 . 老师指出：分数加减混合运算的运算顺序和整数加减混合运算的运算顺序相同。设计意图这一环节，通过形象生动的课件，激发学生的学习兴趣，不仅温习了旧知，而且也为学生学习新知架起了桥梁。真正起到了承上启下

2、的作用二、探究新知1 出示例1 的表格。地貌类型占公园面积的几分之几乔木林灌木丛草地(1)从表格中你能得到哪些数学信息？表中各分数表示什么意思？(2）你能提出那些数学问题？生：乔木林比灌木丛多几分之几？乔木林比草地多几分之几？乔木林、灌木丛和草地共占公园面积的几分之几？(3）老师出示一个问题：“森林部分比草地部分多几分之几？" (4）提问：森林部分指什么？怎样列式？(5）请学生试着算一算，集体交流计算方法。技术官员村位于位于亚运城东部，主干道二以东石楼涌以西的地块，占地面积、m2，总建筑面积、m2，共包括地下室南区、地下室北区、地上部分1栋12栋、服务中心、室外工程等多个单体工程。其

3、中住宅面积m2，共12栋，17栋建筑层数为11层，812栋11层（局部复式顶层），首层局部架空，布置公建配套设施。integrated energy, chemicals and textile yibin city, are the three core pillars of the industry. in 2014, the wuliangye brand value to 73.58 billion yuan, the city's liquor industry slip to stabilise. promoting deep development of integrat

4、ed energy, advanced equipment manufacturing industry, changning district, shale gas production capacity reached 277 million cubic metres, built the country's first independent high-yield wells and pipelines in the first section, the lead in factory production and supply to the population. 2.1-3

5、gdp growth figure 2.1-4 yibin, yibin city, yibin city, fiscal revenue growth 2.1.4 topography terrain overall is southwest, north-eastern state. low mountains and hills in the city landscape as the main ridge-and-valley, pingba small fragmented nature picture for "water and the second land of t

6、he seven hills". 236 meters to 2000 meters above sea level in the city, low mountain, 46.6% hills 45.3%, pingba only 8.1%. 2.1.5 development of yibin landscapes and distinctive feature in the center of the city, with limitations, and spatial structure of typical zonal group, 2012-cities in buil

7、ding with an area of about 76.2km2. from city-building situation, "old town-the south bank" center construction is lagging behind, disintegration of the old city is slow, optimization and upgrading, quality public service resources are still heavily concentrated in the old town together. s

8、outhbank centre has not been formed, functions of the service area space is missing. meanwhile, peripheral group centres service was weak and inadequate accounting for city development, "suspicious" pattern could not be formed. as regards transport, with the outward expansion of cities, ci

9、ties have been expanding, centripetal city traffic organization has not changed, integrated energy, chemicals and textile yibin city, are the three core pillars of the industry. in 2014, the wuliangye brand value to 73.58 billion yuan, the city's liquor industry slip to stabilise. promoting deep

10、 development of integrated energy, advanced equipment manufacturing industry, changning district, shale gas production capacity reached 277 million cubic metres, built the country's first independent high-yield wells and pipelines in the first section, the lead in factory production and supply t

11、o the population. 2.1-3 gdp growth figure 2.1-4 yibin, yibin city, yibin city, fiscal revenue growth 2.1.4 topography terrain overall is southwest, north-eastern state. low mountains and hills in the city landscape as the main ridge-and-valley, pingba small fragmented nature picture for "water

12、and the second land of the seven hills". 236 meters to 2000 meters above sea level in the city, low mountain, 46.6% hills 45.3%, pingba only 8.1%. 2.1.5 development of yibin landscapes and distinctive feature in the center of the city, with limitations, and spatial structure of typical zonal gr

13、oup, 2012-cities in building with an area of about 76.2km2. from city-building situation, "old town-the south bank" center construction is lagging behind, disintegration of the old city is slow, optimization and upgrading, quality public service resources are still heavily concentrated in

14、the old town together. southbank centre has not been formed, functions of the service area space is missing. meanwhile, peripheral group centres service was weak and inadequate accounting for city development, "suspicious" pattern could not be formed. as regards transport, with the outward

15、 expansion of cities, cities have been expanding, centripetal city traffic organization has not changed,方法（一） +-=+-=-=-=方法（二）+-= +-= -= ( 5 ）小结计算方法：计算分数加减混合运算时，可以分步通分也可以一次通分进行计算。计算时，可以根据题目的特点和自己的情况灵活选择方法。设计意图 让学生体会到把异分母分数化成同分母分数的必要，即只有相同单位才能直接相加。再者通过学生自己对两种方法的比较，灵活选择简便的计算方法。2 出示例1 的第二个问题：“裸露地面储存的地下水

16、占降水量的几分之几？( l ）先让学生看懂表格内容，然后老师提问：在这个问题中，把什么看作单位“1 " ？是什么意思？ ( 2 ）请学生列出算式：1 或1 ( ) ( 3 ）请学生试着计算，并指名板演这两种方法的计算过程。1 1 ( ) = =1 ( ) = =1 = 提问：比较这两种方法有什么不同？带有小括号的分数加减混合运算该怎样计算？3 小结。提问：你能说一说分数加减混合运算的顺序吗？引导学生归纳概括出：分数加减混合运算与整数加减混合运算的顺序相同，也是按照从左往右的顺序计算，带有小括号的先算小括号里面的，再算小括号外面的。 设计意图：这一环节，在学生原有知识经验的基础上，放手

17、让学生自己去探索分数加减混合运算的方法，鼓励学生相互交流，然后全班交流，进而探讨分数加减混合运算的计算顺序。三、巩固练习、深化提高。1 完成教材第118页的“做一做。学生试着独立完成，集体交流计算过程，重点看运算顺序及书写美观情况。2 完成教材第120 页练习二十三的第1 4 题。学生独立完成，集体订正。第2 4 题，鼓励学生用不同的方法解答。3某市举办一次数学竞赛，设一、二、三等奖若干名。获一、二等奖的占获奖总人数的，获二、三等奖的占获奖总人数的。获二等奖的占获奖总人数的几分之几？设计意图让学生小组分工合作提出问题、解决问题，亲身体验合作学习的快乐和成功的喜悦。在巩固应用中进一步掌握分数加减

18、混合运算的计算顺序，提高计算的准确率和速度。四、梳理知识，总结升华1、这节课的学习你有什么收获？2、本节课的学习对你有什么帮助或启示？3、你这节课的表现如何？你觉得还有哪些的同学表现比较棒？ 设计意图这一环节的设计，起到提纲挈领的作用。先对学生本堂课的表现给予了肯定和表扬，以增强学生学好数学的信心。接着，让学生用自己的语言说说学到了什么本领，既让学生巩固了所学知识，又培养了学生的综合、概括能力。最后，让学生提醒大家计算时还应该注意什么，一方面给优等生提供了展示的机会，另一方面也让全班学生对本堂课所学的重点、难点和容易发生错误之处得以回顾和反思，有利于知识的掌握、理解和深化。五、课堂检测课堂检测a一、 填空1、0.63里面有63个（）分之一，化成分数是。2、把0.7、0.25、这六个数按从大到小的顺序排列。3、把5克盐放进45克水里，盐占盐水的。二、计算下列各题，（6分）（）三、解决问题1、一个加工厂，第一天加工饲料吨，比第二天少加工吨，两天一共加工多少吨饲料？2、一块地的面积约公顷，其中的种玫瑰花，种郁金香，其余的部分种杜鹃花，种杜鹃花占总面积的几分之几？ 课堂检测b一、解方程。（8分）x=1 x= 4x0.8x=6.4 5x5×11195二、列式计算（或列方程）。（5分）（1）从1