解:
①(
-
)×(
+
),
=
×
,
=
;
②
÷7+
×
,
=
×
+
×
,
=(
+
)×
,
=
×
,
=
;
③2
×
+
÷
,
=2
×
+
×
,
=(2
+
)×
,
=3×
,
=
;
④
÷[
×(
+
)],
=
÷[
×
],
=
÷
,
=
;
⑤
×
+
×
+
,
=
×(
+
+1),
=
×2,
=
;
⑥99×
,
=(100-1)×
,
=100×
-1×
,
=99-
,
=98
;
⑦100×
,
=(99+1)×
,
=99×
+1×
,
=98+
,
=98
.
分析:①先算小括號(hào)里面的減法和加法,再算乘法;
②把
÷7改寫(xiě)為
×
,再根據(jù)乘法分配律進(jìn)行簡(jiǎn)算即可;
③把
÷
改寫(xiě)為
×
,再根據(jù)乘法分配律進(jìn)行簡(jiǎn)算即可;
④先算加法,再算乘法,最后算除法;
⑤根據(jù)乘法分配律進(jìn)行簡(jiǎn)算即可;
⑥把99看作100-1,再根據(jù)乘法分配律進(jìn)行簡(jiǎn)算即可;
⑦把100看作99+1,再根據(jù)乘法分配律進(jìn)行簡(jiǎn)算即可.
點(diǎn)評(píng):分?jǐn)?shù)四則混合運(yùn)算,先弄清運(yùn)算順序,然后再進(jìn)一步計(jì)算即可,能簡(jiǎn)算的要簡(jiǎn)算.