21×17/20(简便算法) 19/54×53(简便运算)

问题描述:

21×17/20(简便算法) 19/54×53(简便运算)

21×17/20
=(20+1)×17/20
=20×17/20+1×17/20
=17+17/20
=17又17/20
19/54×53
= 19/54×(54-1)
=19/54×54-19/54×1
=19-19/54
=18+(1-19/54)
=18又35/54