1、巧算誰(shuí)是贏家,口算第一關(guān),48,92,44,81,48,22,15,38,口算第二關(guān),29,29,29,29,+1,+1,-1,-1,+1,-1,不變,不變,不變,一個(gè)加數(shù)加幾，另一個(gè)加數(shù)減幾，和不變。,61,61,61,61,+5,+5,-5,-5,+5,-5,不變,不變,不變,口算第三關(guān),41,41,41,41,+1,+1,+1,+1,+1,+1,不變,不變,不變,被減數(shù)和減數(shù)同時(shí)加上或減去同一個(gè)數(shù)，差不變。,43,43,43,43,-5,-5,-5,-5,-5,-5,不變,不變,不變,一起算一算： 26+18= 25+19= 24+20=,44,44,44,哪題算得最快？,20,加整十?dāng)?shù)

2、算的更快！,+1,15,-1,85,43,93,+2,-2,40,15,55,+2,-2,將一個(gè)加數(shù)變成整十?dāng)?shù)就容易多了！,再來(lái)算一算： 95-28= 96-29= 97-30=,67,67,67,哪題算得最快？,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,將減數(shù)變成整十?dāng)?shù)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：將一

3、個(gè)加數(shù)變成整十?dāng)?shù)就容易了 兩個(gè)加數(shù)一加一減 減法：將減數(shù)變成整十?dāng)?shù)就容易了 被減數(shù)和減數(shù)同加同減,本課小結(jié):,巧算誰(shuí)是贏家,口算第一關(guān),48,92,44,81,48,22,15,38,口算第二關(guān),29,29,29,29,+1,+1,-1,-1,+1,-1,不變,不變,不變,一個(gè)加數(shù)加幾，另一個(gè)加數(shù)減幾，和不變。,61,61,61,61,+5,+5,-5,-5,+5,-5,不變,不變,不變,口算第三關(guān),41,41,41,41,+1,+1,+1,+1,+1,+1,不變,不變,不變,被減數(shù)和減數(shù)同時(shí)加上或減去同一個(gè)數(shù)，差不變。,43,43,43,43,-5,-5,-5,-5,-5,-5,不變,不變,

4、不變,一起算一算： 26+18= 25+19= 24+20=,44,44,44,哪題算得最快？,20,加整十?dāng)?shù)算的更快！,+1,15,-1,85,43,93,+2,-2,40,15,55,+2,-2,將一個(gè)加數(shù)變成整十?dāng)?shù)就容易多了！,再來(lái)算一算： 95-28= 96-29= 97-30=,67,67,67,哪題算得最快？,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,將減數(shù)變成整十?dāng)?shù)就容易多了！,填一填,3814 =, =,40,52,52,12,6431 =, =,65,95,95,30,5119 =, =,52,32,32,20,4932 =, =,47,17,17,3