①0.3×2.5×0.4 =0.3×(2.5×0.4) =0.3×1 =0.3; ②0.78×101 =0.78×(100+1) =0.78×100+0.78 =78+0.78 =78.78; ③2.5×(8+0.4) =2.5×8+2.5×0.4 =20+1 =21; ④1.25×0.7×0.8 =(1.25×0.8)×0.7 =1×0.7 =0.7; ⑤9.8×2.5 =(10-0.2)×2.5 =10×2.5-0.2×2.5 =25-0.5 =24.5; ⑥50.8×101-50.8 =50.8×(101-1) =50.8×100 =5080; ⑦4.6×99+4.6 =4.6×(99+1) =4.6×100 =460; ⑧0.25×32×0.125 =0.25×4×8×0.125 =(0.25×4)×(8×0.125) =1×1 =1; ⑨38.2×8+61.8×8 =(38.2+61.8)×8 =100×8 =800. |