解:(1)51.6÷[(3
-1.25)×
],
=51.6÷[(3.4-1.25)×
],
=51.6÷[2.15×
],
=51.6÷1.72,
=30;
(2)
×4.8÷(
÷
+0.2),
=6÷(
×
+0.2),
=6÷(2.2+0.2),
=6÷2.4,
=2.5;
(3)(5
-1.8)÷[(1.15+
)×1
],
=(5.4-1.8)÷[(1.15+0.65)×1
],
=3.6÷[1.8×
],
=3.6÷3,
=1.2;
(4)2x-1.65+2.35=7-
x,
2x+0.7=7-0.1x,
2x+0.7-0.7=7-0.1x-0.7,
2x=6.3-0.1x,
2x+0.1x=6.3-0.1x+0.1x,
2.1x=6.3,
2.1x÷2.1=6.3÷2.1,
x=3.
分析:(1)先算小括号内的,再算中括号内的,最后算括号外的;
(2)先算括号外的乘法和括号内的除法,再算括号内的加法,最后算括号外的除法;
(3)先算小括号内的,再算中括号内的,最后算括号外的除法;
(4)原式变为2x+0.7=7-0.1x,根据等式的性质,两边同减去0.7,得2x=6.3-0.1x;两边同加上0.1x,得2.1x=6.3,两边再同除以2.1即可.
点评:考查了四则混合运算和解方程,注意运算顺序和运算法则,在解方程时,注意根据等式的性质进行解答.