二年级数学下册 6.4《巧算》课件2 沪教版.ppt

巧算谁是赢家,口算第一关,48,92,44,81,48,22,15,38,口算第二关,29,29,29,29,+1,+1,-1,-1,+1,-1,不变,不变,不变,一个加数加几，另一个加数减几，和不变。,61,61,61,61,+5,+5,-5,-5,+5,-5,不变,不变,不变,口算第三关,41,41,41,41,+1,+1,+1,+1,+1,+1,不变,不变,不变,被减数和减数同时加上或减去同一个数，差不变。,43,43,43,43,-5,-5,-5,-5,-5,-5,不变,不变,不变,一起算一算： 26+18= 25+19= 24+20=,44,44,44,哪题算得最快？,20,加整十数算的更快！,+1,15,-1,85,43,93,+2,-2,40,15,55,+2,-2,将一个加数变成整十数就容易多了！,再来算一算： 95-28= 96-29= 97-30=,67,67,67,哪题算得最快？,30,20,+1,+1,74,54,20,+2,+2,66,46,20,+3,+3,59,39,20,+1,+1,68,48,30,+5,+5,49,19,将减数变成整十数就容易多了！,填一填,3814 =, =,40,52,52,12,6431 =, =,65,95,95,30,5119 =, =,52,32,32,20,4932 =, =,47,17,17,30,巧算 加法：将一个加数变成整十数就容易了 两个加数一加一减 减法：将减数变成整十数就容易了 被减数和减数同加同减,本课小结:,巧算谁是赢家,口算第一关,48,92,44,81,48,22,15,38,口算第二关,29,29,29,29,+1,+1,-1,-1,+1,-1,不变,不变,不变,一个加数加几，另一个加数减几，和不变。,61,61,61,61,+5,+5,-5,-5,+5,-5,不变,不变,不变,口算第三关,41,41,41,41,+1,+1,+1,+1,+1,+1,不变,不变,不变,被减数和减数同时加上或减去同一个数，差不变。,43,43,43,43,-5,-5,-5,-5,-5,-5,不变,不变,不变,一起算一算： 26+18= 25+19= 24+20=,44,44,44,哪题算得最快？,20,加整十数算的更快！,+1,15,-1,85,43,93,+2,-2,40,15,55,+2,-2,将一个加数变成整十数就容易多了！,再来算一算： 95-28= 96-29= 97-30=,67,67,67,哪题算得最快？,30,20,+1,+1,74,54,20,+2,+2,66,46,20,+3,+3,59,39,20,+1,+1,68,48,30,+5,+5,49,19,将减数变成整十数就容易多了！,填一填,3814 =, =,40,52,52,12,6431 =, =,65,95,95,30,5119 =, =,52,32,32,20,4932 =, =,47,17,17,30,巧算 加法：将一个加数变成整十数就容易了 两个加数一加一减 减法：将减数变成整十数就容易了 被减数和减数同加同减,本课小结:,