估算.91×8≈ 52×3≈ 398×8≈ 201×3≈ 9×898≈ 502×7≈82×7≈ 39×6≈ 89×6≈ 701×4≈ 699×7≈ 198×2≈
4-0.8÷4-0.8 19.98×37-199.8×1.9+1998×0.82
73.8×16-73.8×6 (0.125×8-0.5)÷0.25
3.5×(20.6-16.8÷4.8) 16.2÷(3.2×0.25+4.6)
2.5÷[(17.2-4.5×3.6)÷0.04] 4.5÷0.25-0.75×1.2
(66-32×1.2)÷0.25 12.5×(1618-8.4÷0.12)