简算:①()×36②2.5×(1.9+1.9+1.9+1.9)
估算:398÷4≈ 813÷9≈ 197÷5≈22×49≈ 59×61≈ 91×22≈
估算:603×39≈ 396×41≈ 390÷21≈ 478÷78≈
估一估,算一算.61×21≈ 99×28≈ 12×57≈52×19≈ 195÷4≈ 88÷3≈241÷6≈ 440÷9≈
估算下列各题.405×21≈197×6≈2410÷81≈23×28≈2030÷41≈8970÷89≈409×99≈8130÷91≈
估一估、算一算.29×8≈ 51×7≈ 201×6≈ 318×4≈