7.81*49-78.1*3.8+0.781*90简算

7.81*49-78.1*3.8+0.781*90简算
2025-03-02 12:35:59
推荐回答(4个)
回答1:

利用乘法分配律的逆运算进行简便运算:

7.81×49-78.1×3.8+0.781×90

=7.81× 49-7.81×10×3.8+7.81×0.1×90

=7.81× 49-7.81× 38+7.81× 9

=7.81×(49-38+9)

=7.81×20

=156.2

扩展资料:

数学中乘法运算应当遵循的运算定律:

1、乘法交换律:两个数相乘,交换两个因数的位置,积不变。

用字母表示:a×b=b×a。

2、乘法结合律:三个数相乘,先乘前两个数,或者先乘后两个数,积不变。

用字母表示:(a×b)×c=a×(b×c)。

3、乘法分配律:两个数的和与一个数相乘,可以先把它们与这个数分别相乘,再相加。

用字母表示:(a+b)×c=a×c+b×c。

回答2:

7.81*49-78.1*3.8+0.781*90

=7.81*49-7.81*38+7.81*9
=7.81*(49-38+9)
=7.81*(11+9)
=7.81*20
=156.2

回答3:

解:7.81*49-78.1*3.8+0.781*90
=78.1*4.9-78.1*3.8+78.1*0.9
=78.1*(4.9-3.8+0.9)
=78.1*2
=156.2

回答4:

7.81*49-78.1*3.8+0.781*90=7.81*49-7.81*38+7.81*9=7.81*(49-38+9)=7.81*20=156.2

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