分析:①②⑤⑥运用乘法的分配律进行计算即可;
③运用一个数连续除以2个数,可以用这个数除以这两个数的积;
④把3.2拆成8×0.4运用乘法的结合律、交换律进行计算即可.
⑦把0.35=7×0.05,然后用5.6除以7得到的商再除以0.05即可.
算式⑧根据四则混合运算的运算顺序计算即可.
解答:解:①1.2×0.25+2.8×0.25
=0.25×(1.2+2.8)
=0.25×4
=1;
②0.65×104
=0.65×(100+4)
=0.65×100+0.65×4
=65+2.6
=67.6;
③16.8÷40÷0.25
=16.8÷(40×0.25)
=16.8÷10
=1.68;
④3.2×1.25×2.5
=8×0.4×1.25×2.5
=(8×1.25)×(0.4×2.5)
=10×1
=10;
⑤2.8×3.6+28×0.64
=28×0.36+28×0.64
=28×(0.36+0.64)
=28×1
=28;
⑥1.25×8.08
=1.25×(8+0.08)
=1.25×8+1.25×0.08
=10+0.1
=10.1;
⑦5.6÷0.35
=5.6÷7÷0.05
=0.8÷0.05
=16;
⑧20.9+10.5÷(5.2-4.5)
=20.9+10.5÷0.7
=20.9+15
=35.9.
点评:完成本题要注意分析式中数据,运用合适的简便方法计算,注意认真解答即可.