解:①[3.2×(1-
)+3
]×2
,
=[3
×(1-
)+3
]×2
,
=[3
×
+3
]×2
,
=(
)×
,
=
×
,
=10;
②1
+2
+4
+3
,
=(1
+4
)+(2
+3
),
=6+5
,
=11
;
③
×99,
=
×(97+2),
=
×97+
×2,
=43+
,
=43
;
④3.75×4
+1.6×3
,
=3.75×4.4+1.6×3.75,
=3.75×(4.4+1.6),
=3.75×6,
=22.5;
⑤1÷2.5+2.5×0.4,
=0.4+2.5×0.4,
=0.4×(1+2.5),
=0.4×3.5,
=1.4;
⑥3
-1
-
,
=3
-(1
+
),
=3
-2,
=
.
分析:①把小數(shù)化成分?jǐn)?shù),按四則混合運(yùn)算的順序計(jì)算;
②利用加法的交換和結(jié)合律;
③先把99分成97+2,然后利用乘法的分配律;
④先把分?jǐn)?shù)化成小數(shù),然后利用乘法的分配律計(jì)算;
⑤先按四則運(yùn)算,算出第一步結(jié)果后,再用乘法分配律;
⑥運(yùn)用連減的簡(jiǎn)算.
點(diǎn)評(píng):這幾道題主要考查乘法的分配律、加法的交換律和結(jié)合律、連減的簡(jiǎn)算以及按四則混合運(yùn)算順序計(jì)算.