1.12×（分母是3×9,分子是1+分母是9×15,分子是1+分母是15×21,分子是
1+分母是21×27,分子是1+分母是27×33,分子是1）
=12×[1/6×(1/3-1/9)+1/6×(1/9-1/15)+1/6×(1/15-1/21)+1/6×(1/21-1/27)+1/6×(1/27-1/33)]
=12×[1/6×(1/3-1/9+1/9-1/15+1/15-1/21+1/21-1/27+1/27-1/33)]
=12×1/6×(1/3-1/33)
=2×10/33
=20/33
2.（4.8×7.5×8.1）÷（2.4×2.5×2.7）
=(2.4×2×2.5×3×2.7×3)÷(2.4×2.5×2.7)
=(2.4×2.5×2.7×2×3×3)÷(2.4×2.5×2.7)
=2×3×3
=18
3.3.75×4.8+62.5×0.48
=3.75×4.8+6.25×10×0.48
=3.75×4.8+6.25×4.8
=(3.75+6.25)×4.8
=10×4.8
=48