21*39+87*39-39*9怎么简便算

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21*39+87*39-39*9怎么简便算
21*39+87*39-39*9怎么简便算

21*39+87*39-39*9怎么简便算
21*39+87*39-39*9
=39×(21+87-9)
=39×100
=3900

=39*(21+87-39+1-1)
=39*60-39
=2301

21*39+87*39-39*9
=39(21+87-9)
=39*99
=39*100-39
=3900-39
=3861

21*39+87*39-39*9
=39×(21+87-9)
=39×100
=3900