沪教版二年级下册数学 巧算

1、教学目标,将两位数运算中的巧算方,法迁移到三位数运算中来,学会运用加法交换律与结,合律进行巧算,18+25+35,23+49+17,92-36-24,67-19-17,比一比，谁算得快,18+25+35,23+49+17,92-36-24,67-19-17,比一比，谁算得快,78,18+25+35,23+49+17,92-36-24,67-19-17,比一比，谁算得快,78,89,18+25+35,23+49+17,92-36-24,67-19-17,比一比，谁算得快,78,89,32,18+25+35,23+49+17,92-36-24,67-19-17,比一比，谁算得快,78,89,32,

2、31,18+25+35,23+49+17,92-36-24,67-19-17,比一比，谁算得快,78,89,32,31,说说你怎,么算得,这么快,18+25+35,23+49+17,92-36-24,67-19-17,比一比，谁算得快,78,89,32,31,说说你怎,么算得这,么快,凑整十数,18+25+35,23+49+17,92-36-24,67-19-17,比一比，谁算得快,78,89,32,31,说说你怎,么算的这,么快,凑整十数,能凑成整十数的两个两位数有什么特点,探究一,探究二,实验小学举行“献爱心活动”，为灾,区贫困儿童送礼物，二年级全体师生共筹集,捐款,758,元,准备去商店

3、买这样三件礼物,请,你帮忙算一算，够不够？为什么,237,元,389,元,163,元,探究一,例,1,389+163+237,探究一,探究二,例,1,389+163+237,可以巧算吗？那两个数,能凑成整百数,探究一,探究一,探究二,例,1,389+163+237,可以巧算吗？那两个数,能凑成整百数,389,163+237,探究一,探究一,探究二,例,1,389+163+237,389,163+237,389+400,探究一,可以巧算吗？那两个数,能凑成整百数,探究一,探究二,例,1,389+163+237,可以巧算吗？那两个数,能凑成整百数,389,163+237,389+400,789,探

4、究一,探究一,探究二,例,1,389+163+237,可以巧算吗？那两个数,能凑成整百数,389,163+237,389+400,789,1,为什要把,163,和,237,先加,探究一,例,1,389+163+237,可以巧算吗？那两个数,能凑成整百数,389,163+237,389+400,789,元,1,为什要把,163,和,237,先加,2,小括号有什么作用,探究一,478+243+222,478+243+222,478+222,243,700+243,943,478+243+222,1,478,和,222,为什么先加,478+222,243,700+243,943,478+243+22

5、2,1,478,和,222,为什么先加,478+222,243,700+243,943,2,这两个数中间还夹着一个,243,怎么办,478+243+222,1,478,和,222,为什么先加,478+222,243,700+243,943,2,这两个数中间还夹着一个,243,怎么办,3,巧算的关键是什么,478+243+222,1,478,和,222,为什么先加,478+222,243,700+243,943,2,这两个数中间还夹着一个,243,怎么办,3,巧算的关键是什么,凑整百数,判断：能不能巧算,1,358+227+142 (,2,216+253+129 (,3,131+235+165

6、(,判断：能不能巧算,1,358+227+142 (,2,216+253+129 (,3,131+235+165 (,358+227+142 (,2,216+253+129 (,3,131+235+165 (,判断：能不能巧算,1,358,227,142,358+227+142 (,2,216+253+129 (,3,131+235+165 (,判断：能不能巧算,1,358,227,142,358+227+142 (,2,216+253+129 (,3,131+235+165 (,判断：能不能巧算,1,358,227,142,358+227+142 (,2,216+253+129 (,131+

7、235+165 (,3,131,235+165,判断：能不能巧算,1,358,227,142,讨论：凑成整百数的两个三位数有什么,特点,例,2,853-498-253,探究二,例,2,853-498-253,600-498,102,853-253,498,探究二,例,2,853-498-253,为什么要先算,853,253,600-498,102,853-253,498,探究二,例,2,853-498-253,为什么要先算,853,253,600-498,102,试一试,652-376-52,853-253,498,探究二,例,2,853-498-253,为什么要先算,853,253,600-

8、498,102,试一试,652-376-52,652-52-376,600-376,224,853-253,498,探究二,例,2,853-498-253,为什么要先算,853,253,600-498,102,试一试,652-376-52,652-52-376,600-376,224,853-253,498,探究二,278+374+226 554-217-83,183+99+117 376-199-176,278+374+226 554-217-83,183+99+117 376-199-176,278+(374+226,278+600,578,278+374+226 554-217-83,183+99+117 376-199-176,278+(374+226,278+600,578,554,217+83,554-300,154,278+374+226 554-217-83,183+99+117 376-199-176,278+(374+226,278+600,578,183+117+99,300+99,399,554,217+83,554-300,154,278+374+226 553-267-83,183+99+117 376-199-176,278+(374+226,278+600,578,183+117+99,300+9