=.=公因就3/11吧
^_^最简单当然就是按计算机啦
14/15*3/11+13/14*5/11
=(1-1/15)*3/11+(1-1/14)*5/11
=3/11-1/15*3/11+5/11-1/14*5/11
=8/11-(1/5-5/14)*1/11
=8/11-(-11/70)*1/11
=8/11+1/70
=571/770
14/15X3/11+13/14X5/11
=(1-1/15)X3/11+(1-1/14)X5/11
=3/11-1/15X3/11+5/11-1/14X5/11
=8/11-(1/5-5/14)X1/11
=8/11-(-11/70)X1/11
=8/11+1/70
=571/770