解:(1)1.05×(3.8-0.8)÷6.3,
=1.05×3÷6.3,
=0.5;
(2)9
÷1
+5.46÷2
×(4.875-2
),
=
×
+5.46×
×(4.875-2.875),
=
+5.46×
×2,
=5.8+4.2,
=10;
(3)2.51×10
2+251÷
÷(
×0.1),
=2.51×100+251×
÷(0.2×0.1),
=251+10÷0.02,
=251+500,
=751;
(4)28×(
+
)-223×(
-
)+251×(
-
),
=28×
+28×
-223×
+223×
+251×
-251×
,
=(
+
)-(
-
)+(
-
)
=1-1+1,
=1.
分析:(1)按運(yùn)算順序進(jìn)行計(jì)算,從左向右依次計(jì)算;
(2)按運(yùn)算順序進(jìn)行計(jì)算,先算除法和括號(hào)內(nèi)的,再算加法,但要注意數(shù)字的變化;
(3)先算平方,再算括號(hào)內(nèi)的,然后算乘法和除法;
(4)先運(yùn)用乘法分配律計(jì)算,然后再運(yùn)用加法交換律與結(jié)合律簡(jiǎn)算.
點(diǎn)評(píng):此題應(yīng)注意運(yùn)算順序,同時(shí)考查了運(yùn)算定律的使用以及平方數(shù)的計(jì)算.