解:(1)
-
-
-
-
-
-
,
=
-(
-
)-(
-
)-(
-
)-(
-
)-(
-
)-(
-
),
=
;
(2)[1.25+(1
÷
-2.5÷3
)]÷25%,
=[
+(
×
-
×
)]÷
,
=[
+(
-
)]÷
,
=[
+
]÷
,
=
×4,
=
;
(3)
-
+
-
+
-
,
=1+
-(
+
)+(
+
)-(
+
)+(
+
)-(
+
),
=1+
-
-
+
+
-
-
+
+
-
-
,
=1-
,
=
;
(4)81
×
+71
×
+61
×
+51
×
+41
×
+31
×
,
=(80+
)×
+(70+
)×
+(60+
)×
+(50+
)×
+(40+
)×
+(30+
)×
,
=70+1+60+1+50+1+40+1+30+1+20+1
=(70+60+50+40+30+20)+6,
=270+6,
=276.
分析:(1)通過觀察,從第二個分數(shù)開始,每個分數(shù)都可以拆成兩個分數(shù)相減的形式,然后通過分數(shù)加減相抵消的方法,求得結果;
(2)把小數(shù)和百分數(shù)化為分數(shù),先計算小括號內(nèi)的除法,再計算小括號內(nèi)的減法,然后算中括號內(nèi)的加法,最后算括號外的除法;
(3)通過觀察,把每個分數(shù)可以拆成兩個分數(shù)相加的形式,然后通過分數(shù)加減相抵消的方法,求得結果;
(4)通過觀察,把每個分數(shù)可以拆成整十數(shù)和假分數(shù)的形式,運用乘法分配律簡算.
點評:完成本題應注意分數(shù)的拆分,靈活運用運算技巧,進行簡便計算.