解题思路:(1)(4)(11)(12)根据四则混合运算中,有括号的先算括号里面的,再算括号外面的计算即可;
(2)(3)根据乘法的交换律与结合律解答即可;
(5)(6)(8)(10)根据乘法的分配律解答即可;
(7)根据减法的性质以及加法的结合律简算;
(9)根据除法的性质以及乘法的交换律与结合律简算.
(1)3-(12.9-84×[1/7])
=3-(12.9-12)
=3-0.9
=2.1
(2)44.4×25
=11.1×(4×25)
=11.1×100
=1110
(3)[40/13]×(26×[3/40])
=([40/13]×[3/40])×26
=[3/13×26
=6
(4)2-[
1
6]+([3/4]-[7/10])]
=2-[[1/6]+[1/20]]
=2-[13/60]
=1[47/60]
(5)7.25×1.8+27.5×0.18
=7.25×1.8+2.75×1.8
=(7.25+2.75)×1.8
=10×1.8
=18
(6)905×99+905
=905×(99+1)
=905×100
=90500
(7)[([14/19]-[5/13])+([5/19]-[8/13])]÷[11/12]
=[([14/19]+[5/19])-([5/13]+[8/13])]÷[11/12]
=[1-1]÷
11
12
=0÷
1
12
=0
(8)34×([1/17]+[1/13])×13
=34×13×[1/17]+[1/13]×13×34
=26+34
=60
(9)2000÷12.5÷25÷0.8÷4
=2000÷(12.5×25×0.8×4)
=2000÷[(12.5×0.8)×(25×4)]
=2000÷1000
=2
(10)[2/5]×[11/15]+[2/5]÷[15/4]
=[2/5]×[11/15]+[2/5]×[4/15]
=[2/5]×([11/15]+[4/15])
=[2/5×1
=
2
5]
(11)[([4/5]-[1/4])×[6/11]]÷[9/20]
=[[11/20]×[6/11]]÷[9/20]
=[3/10×
20
9]
=[2/3]
(12)([1/2]+[1/4])÷([4/5]÷4-[1/10])
=[3/4]÷([1/5]-[1/10])
=[3/4÷
1
10]
=[15/2]
点评:
本题考点: 整数、分数、小数、百分数四则混合运算;运算定律与简便运算.
考点点评: 考查了运算定律与简便运算,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简便计算.