解:(1)12×(
+
-
)
=12×
+12×
-12×
,
=2+3-4,
=1;
(2)48×
,
=(49-1)×
,
=49×
-1×
,
=1-
,
=
;
(3)3.7×
+5.3×0.75+
,
=3.7×0.75+5.3×0.75+0.75,
=0.75×(3.7+5.3+1),
=0.75×10,
=7.5;
(4)9.9+99.9+999.9,
=(10-0.1)+(100-0.1)+(1000-0.1),
=(10+100+1000)-(0.1+0.1+0.1),
=1110-0.3,
=1109.7.
分析:(1)運(yùn)用乘法發(fā)分配律簡(jiǎn)算;
(2)把48看作(49-1),運(yùn)用乘法發(fā)分配律簡(jiǎn)算;
(3)把分?jǐn)?shù)化為小數(shù),運(yùn)用乘法發(fā)分配律簡(jiǎn)算;
(4)根據(jù)數(shù)字特點(diǎn),把原式變?yōu)椋?0-0.1)+(100-0.1)+(1000-0.1),運(yùn)用加法結(jié)合律簡(jiǎn)算.
點(diǎn)評(píng):此題主要考查分?jǐn)?shù)、小數(shù)的四則混合運(yùn)算,注意應(yīng)用運(yùn)算定律進(jìn)行簡(jiǎn)便計(jì)算.