解:①(
+
)÷(
-
),
=
÷
,
=
,
=
;
②[19.8-(4.9+9.8)]×(1÷0.01),
=[19.8-14.7]×100,
=5.1×100,
=510;
③155×360×77÷90÷11÷31,
=(155÷31)×(360÷90)×(77÷11),
=5×4×7,
=140;
④1÷28×72-27×
-17÷28,
=
72-27×
-17×
,
=
(72-27-17),
=
28,
=1.
分析:①(
+
)÷(
-
),先算括號(hào)里面的,異分母分?jǐn)?shù)加、減法,先通分,再按照同分母分?jǐn)?shù)加、減法則進(jìn)行計(jì)算,最后算除法;
②[19.8-(4.9+9.8)]×(1÷0.01),根據(jù)小數(shù)四則混合運(yùn)算的運(yùn)算順序,先算小括號(hào)里面的,再算中括號(hào)里面的,最后算括號(hào)外面的,按照小數(shù)四則運(yùn)算的計(jì)算法則進(jìn)行計(jì)算;
③155×360×77÷90÷11÷31,將運(yùn)算順序調(diào)整為:(155÷31)×(360÷90)×(77÷11)這樣計(jì)算比較簡(jiǎn)便;
④1÷28×72-27×
-17÷28.把除以28轉(zhuǎn)化為乘
,再根據(jù)乘法分配律進(jìn)行簡(jiǎn)算;
點(diǎn)評(píng):此題主要考查整數(shù)、小數(shù)、分?jǐn)?shù)四則混合運(yùn)算.注意運(yùn)算順序和運(yùn)算法則,靈活運(yùn)用所學(xué)的運(yùn)算定律進(jìn)行簡(jiǎn)便計(jì)算.