分析:(1)根據(jù)數(shù)字特點(diǎn),原式變?yōu)?.8×54.6+1.8×45.4,運(yùn)用乘法分配律簡算;
(2)把0.32看作4×0.08,運(yùn)用乘法交換律與結(jié)合律簡算;
(3)運(yùn)用除法的性質(zhì)簡算;
(4)把9.9看作10-0.1,運(yùn)用乘法分配律計(jì)算,然后再加上0.1即可;
(5)運(yùn)用乘法交換律與結(jié)合律簡算;
(6)把10.2看作(10+0.2),運(yùn)用乘法分配律簡算.
解答:解:(1)18×5.46+1.8×45.4,
=1.8×54.6+1.8×45.4,
=1.8×(54.6+45.6),
=1.8×100,
=180;
(2)0.32×0.25×12.5,
=4×0.08×0.25×12.5,
=(4×0.25)×(12.5×0.08),
=1×1,
=1;
(3)21÷0.25÷0.4,
=21÷(0.25×0.4),
=21÷0.1,
=210;
(4)0.2×9.9+0.1,
=0.2×(10-0.1)+0.1,
=2-0.02+0.1,
=2.08;
(5)0.25×4.78×4,
=(0.25×4)×4.78,
=1×4.78,
=4.78;
(6)3.2×10.2,
=3.2×(10+0.2),
=32+0.64,
=32.64.
點(diǎn)評:此題考查了小數(shù)的四則混合運(yùn)算,注意運(yùn)算順序和運(yùn)算法則,靈活運(yùn)用所學(xué)的運(yùn)算定律進(jìn)行簡便計(jì)算.