4吨=千克
2时=分
301×2≈ 298×4≈ 8×403≈ 1﹣ =
56÷7= 25×4= 850﹣240= + =
①408×6=
②462×7=
③811×6=
④723+241= 验算:
⑤850﹣357= 验算: