分析:(1)把99看作98+1,運(yùn)用乘法分配律計算99×
,原式變?yōu)?9+
-
,然后運(yùn)用結(jié)合律簡算;
(2)先算括號內(nèi)的,然后約分即可;
(3)通過觀察,每個分?jǐn)?shù)的分母為兩個連續(xù)自然數(shù)的乘積,因此,每個分?jǐn)?shù)都可以拆成兩個分?jǐn)?shù)相減的形式,然后通過分?jǐn)?shù)的加減相互抵消,求出結(jié)果;
(4)此題應(yīng)通過數(shù)的拆分,運(yùn)用乘法分配律簡算.
解答:解:(1)99×
-
,
=(98+1)×
-
,
=99+
-
,
=99+(
-
),
=99+1,
=100;
(2)(1.25+
)×8×
,
=(1
+
)×8×
,
=
×8×
,
=
;
(3)
+
+
+…+
,
=
-
+
-
+
-
+…+
-
,
=
,
=
;
(4)3.6×42.3×3.75-12.5×0.423×28,
=0.9×4×42.3×3.75-0.125×42.3×7×4,
=0.9×42.3×4×3.75-0.125×4×42.3×7,
=0.9×42.3×15-0.5×42.3×7,
=42.3×(0.9×15-0.5×7),
=42.3×(13.5-3.5),
=42.3×10,
=423.
點評:完成此題,應(yīng)認(rèn)真分析題中數(shù)據(jù),運(yùn)用所學(xué)運(yùn)算定律或運(yùn)算技巧,靈活簡算.