分析:這幾道算式是有關(guān)整數(shù)、小數(shù)、分?jǐn)?shù)的四則混合運(yùn)算,有些題在計(jì)算時要靈活運(yùn)用簡算,如:(1)題把“3001”看作“3000+1”,把“1998”看作“2000-2”;(2)題運(yùn)用加法結(jié)合律;第(3)題運(yùn)用乘法分配律;第(6)題運(yùn)用乘法分配律.
解答:解:(1)3001-1998,
=(3000+1)-(2000-2),
=(3000-2000)+3,
=1003;
(2)3.9+
4+6.1+5,
=(3.9+6.1)+(
4+ 5),
=10+10,
=20;
(3)(
++)×0.24,
=
×0.24+
×0.24+
×0.24,
=0.12+0.08+0.03,
=0.23;
(4)5000-105×34,
=5000-3570,
=1430;
(5)0.15÷0.25+0.75×1.2,
=0.6+0.9,
=1.5;
(6)
[5+( 1-0.2)× 1.5]÷,
=[
5+
×1.5]÷
,
=[
+]×60,
=
×60+×60,
=332+87,
=419.
點(diǎn)評:計(jì)算題一定要審好題,看是否能用簡便算法,簡便計(jì)算主要是利用運(yùn)算定律以及數(shù)與數(shù)之間的特殊關(guān)系靈活進(jìn)行的.