文档介绍：加减混合计算 2 4 +4 8 +1 7 = 24 48 +72 189 72 17 ++1789 89 24 48 72 + 1练一练 8 . 85 29 56 -.85 -29-48= 练一练 85 29 -56 .56 48 -8 .-48 8 5+6-7 8+9-5 12-5+8 14-6+8 29-9+5 15 +8-3口算 68 29 - 68-29+51= 68 29 -39 .39 51 +90 139 .+51 90 1简便算法 90 35 6 +2 4 -3 0 = 6 7 -3 4 +2 9 = 做一做 7 2 - ( 4 7 + 1 6 ) = 447 16 + 163 72 63 -9 .9 3 2 + ( 5 5 - 4 6 ) = 55 46 -9+32 41 41 3 7 + ( 5 0 – 2 6 ) 7 0 - ( 3 5 +2 1 ) 8 5 - ( 3 2 – 1 8 ) 32+ (55 -46) = 76- (13 +42) = 做一做