解:(1)7.8×
+2.2×20%,
=7.8×0.2+2.2×0.2,
=(7.8+2.2)×0.2,
=10×0.2,
=2;
(2)0.5×[5
÷﹙
-
﹚],
=0.5×[
÷
],
=0.5×[
×
],
=0.5×
,
=3.2;
(3)(198+32×72)-2472÷24,
=(198+2304)-103,
=[(200-2)+(2300+4)]-103,
=[200+2300+(4-2)]-103,
=2500+2-(100+3),
=2500-100-(3-2),
=2400-1,
=-2399;
(4)4
×[2.6+
-(0.65+1
)]÷2
,
=4
×[2.6+
-0.65-1
]÷2
,
=4
×[2.6-0.65-(1
-
)]×
,
=
×[1.95-1]×
,
=
×0.95×
,
=1.52.
分析:(1)把分?jǐn)?shù)和百分?jǐn)?shù)化成小數(shù),運(yùn)用乘法分配律的逆運(yùn)算簡(jiǎn)算;
(2)先算下括號(hào)內(nèi)的,再算中括號(hào)內(nèi)的,最后算括號(hào)外的;
(3)先算括號(hào)內(nèi)的乘法和括號(hào)外的2472÷24,得=(198+2304)-103,把198看作200-2,把2304看作2300+4,把103看作100+3,運(yùn)用加法交換律與結(jié)合律簡(jiǎn)算;
(4)中括號(hào)內(nèi)先去小括號(hào),運(yùn)用加法交換律與結(jié)合律簡(jiǎn)算,得
×0.95×
,因?yàn)?.95能與5約分,不用化成分?jǐn)?shù),直接約分即可.
點(diǎn)評(píng):在脫式計(jì)算中,特別注意運(yùn)算順序和運(yùn)算法則,對(duì)分?jǐn)?shù)、小數(shù)、百分?jǐn)?shù)的互化要細(xì)心,根據(jù)題目情況,靈活處理.注意運(yùn)用所學(xué)定律,進(jìn)行簡(jiǎn)算.