口算.
口算: 256800+256600= 256000+365500= 658900+654200= 125600-115600= 2560000-1260000= 15260000-15160000=
口算: 20000+30000= 25000+25000= 35000+25000= 45000-15000= 200000-150000= 120000-20000=
估算: 24560+11260= 21410+21210= 15610+21000= 90410+21060= 95230+21245= 91210+21260=
估算: 705500-50800≈ 5035433-205000≈ 305500-108900≈ 805433+205000≈ 855500-579900≈ 533533-205130≈
估算: 905500-500900≈ 403553-205000≈ 505500-408900≈ 703543-205050≈ 803033-205010≈ 805500-508900≈