900-90= 260+350= 212×4= 72÷8=
28-14÷2= 24×5= 55+35= 68+29=
1001+997≈ 21+579×0= 204×9= 37-19=
2×303= 298×3≈ 120-20×6= + =
1- = + = - = + =1-
验算