12.5×3.2×2.5 =12.5×0.8×4×2.5 =(12.5×0.8)×(4×2.5) =10×10 =100 4.2×101 =4.2×(100+1) =4.2×100+4.2×1 =420+4.2 =424.2 2.73×99+2.73 =2.73×99+2.73×1 =2.73×(99+1) =2.73×100 =273 8.3×9.8+2×0.83 =8.3×9.8+0.2×8.3 =8.3×(9.8+0.2) =8.8×10 =83