脱式计算,能简算的要简算.(1)3-(12.9-84×[1/7])

1个回答

  • 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.