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61×数学公式-1÷17×47+20÷17.

解:61×-1÷17×47+20÷17
=61×-1××47+20×
=61×-47×+20×
=(61-47+20)×
=34×
=2.
分析:本题从原题中不能看出能否用简便算法,看能否用简便算法,先要进行转化,把除法转化为乘法进行,转化为乘法后,进行比较、分析,看出有相同的因数,然后进行提取,运用乘法分换率,得出结论.
点评:看是否能用简便算法进行计算,首先要看这个题是只存在乘法,还是存在乘法和加法;如只存在乘法,首先想到用乘法交换率和乘法结合率;如存在乘法和加法,要想到乘法分配律;如果题中给出的是除法,则要进行转化,进而得出结论.
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