分析:(1)
3×7,把
3看作(3
+),利用乘法分配律比較簡便;
(2)(
+1÷)
÷按運算順序直接計算就可以了;
(3)9×
×先約分,再計算;
(4)
×+×,利用乘法分配律比較簡便;
(5)2.35+
÷+2.35按運算順序計算;
(6)(
+)÷(
- ),先通分,再計算;
(7)(8)(
+)
÷、(
+ -)
÷先轉(zhuǎn)化成乘法,再利用乘法分配律比較簡便;
(9)25÷(
-),先通分,再計算.
解答:解:(1)3
×7,
=(3×7)+(
×7),
=21+
,
=21
;
(2)(
+1÷)÷
,
=(
+1×
)×
,
=(
+
)×
,
=4×
,
=
,
=1
;
(3)9×
×
,
=9×
×
,
=
;
(4)
×
+
×
,
=(
+)×
,
=1×
,
=
;
(5)2.35+
÷+2.35,
=2.35+
×+2.35,
=2.35+2+2.35,
=6.7;
(6)(
+)÷(
-),
=
÷
,
=
×
,
=
,
=
2;
(7)(
+)
÷,
=(
+)×
,
=
×+ ×,
=2
+,
=
3;
(8)(
+-)
÷,
=
×24+
×24-
×24,
=18+4-3,
=19;
(9)25÷(
-),
=25÷(
-),
=25×
,
=180.
點評:計算這類題目,先要認真觀察算式特點,能簡算的要簡算,不能簡算按照混合運算的計算方法進行計算,要靈活處理,分別對待.