估算:69×8≈ 91×9≈ 398×6≈ 5×401≈ 517﹣348≈
8-2= 6+2= 8-6=
6-3= 3+3= 7-5= 5+2=
9-4= 9-5= 4+5=
10-4= 10-6= 4+6=
5+2= 7-5= 7-2=