脱式计算,能简算的要简算.0.8×3.9×1.25 4.87×2.34+4.87×7.66 0.49×9.9 60.8-

1个回答

  • 解题思路:(1)利用乘法交换律和结合律先计算0.8×1.25,再与3.9相乘;

    (2)利用乘法分配律的逆运算进行简便计算;

    (3)把9.9写成10-0.1,再利用乘法分配律计算即可解答;

    (4)根据连减的性质:a-b-c=a-(c+b)进行简便计算即可解答;

    (5)把3.2写成0.4×8,再把2.5和0.4相乘,8和12.5相乘,再把所得的积相乘即可;

    (6)此题没有简便计算的方法,按照运算顺序,先算乘法,再算加法,计算即可.

    (1)0.8×3.9×1.25

    =0.8×1.25×3.9

    =1×3.9

    =3.9

    (2)4.87×2.34+4.87×7.66

    =4.87×(2.34+7.66)

    =4.87×10

    =48.7

    (3)0.49×9.9

    =0.49×(10-0.1)

    =0.49×10-0.49×0.1

    =4.9-0.049

    =4.851

    (4)60.8-7.18-12.82

    =60.8-(7.18+12.82)

    =60.8-20

    =40.8

    (5)2.5×3.2×12.5

    =2.5×(0.4×8)×12.5

    =(2.5×0.4)×(8×12.5)

    =1×100

    =100

    (6)3.95×7.6+2.4

    =30.02+2.4

    =32.42.

    点评:

    本题考点: 小数四则混合运算;运算定律与简便运算.

    考点点评: 完成本题要注意分析式中数据,运用合适的简便方法计算.