=5/21X21/5X22/5
=1X22/5=22/5
=11/15-(2/15+1/2)
=11/15-2/15-1/2
=9/15-1/2
=3/5-1/2
=6/10-5/10=1/10
13/98X99
=13/98X(98+1)
=13+13/98
=13又98分之13
希望能帮你忙,懂了请采纳,五分之四×四+五分之二×二+五分之一×十六对了，要用简便算法还有这道题：二零一零分之二零零九×二零零九【也要用简便算法】最好有过程[求帮助=4/5X4+2/5X2+1/5X16=1/5X16+1/5X4+1/5X16=1/5(16+4+16)=36/5=7又5分之1 =2009/2010X2009=(2010-1)X2009/2010=2009-2009/2010=2008又2010分之1