解:(1)(3
)÷
,
=(3
-4×0.25×
-
)÷
,
=(3
-
-
)÷
,
=(3
-
-
)
,
=(3-
)
,
=
×
,
=
;
(2)
×13+
×24+51
×
,
=
×7+
×24+51
×
,
=
×(7+24)+51
×
,
=
×31+51
×
,
=13+37,
=50;
(3)(3
+4
)×2
,
=
×
,
=
;
(4)
+
-
+
,
=7×(
-
+
-
+
),
=7×(
+
-
-
+
+
-
-
+
+
),
=7×(
+
),
=7×
,
=
.
分析:(1)先把小括号里面的乘法运用乘法结合律简算,再运用减法的性质简算,最后算括号外的除法;
(2)先运用乘法分配律简算,再算最后一个乘法,最后算加法;
(3)先算小括号里面的加法,再算括号外的乘法;
(4)先提取7,变成7×(
-
+
-
+
),再根据
=
-
,
=
+
…进行化简,进而求解.
点评:本题考查了四则混合运算,注意运算顺序和运算法则,灵活运用所学的运算定律进行简便计算.