估算:675500-510900≈703530-205120≈695540-578905≈503543-105780≈595500-478900≈735433-205540≈
210-60= 420+50= 630+40= 880-80= 670+80= 750-80=
240-80= 420+70= 760+80= 870-50= 650+70= 740-70=
120-70= 370+90= 350+80= 910-50= 560+40= 650-70=
27+67= 10×6-8= 39-0÷10=88-23= 45-5×9= 25+0÷5=
77+93= 15×1-7= 39-100÷10=99-77= 23-3×7= 35-35÷5=