(简算)2分之1+6分之5-12分之7+20分之9-30分之11

=(1-1/2) +(1/2+1/3)-(1/3+1/4)+(1/4+1/5)-(1/5+1/6)
=1-1/2+1/2-1/3-1/3-1/4+1/4+1/5-1/5-1/6
=1-1/6
=5/6why要这样做简便方法如11/30=(5+6)/5×6 =6/5×6 +5/5×6=1/5+1/6　　谢谢了。　　靠，原来是这样做的。我做了好几遍的了，我居然不会做。　　请采纳，谢谢