简便计算5/17÷9+1/9x12/17=5/17x1/9+12/17x1/9=(5/17+12/17)x1/9=1x1/9=1/9
7/15÷9+1/9×12/17=7/15×1/9+1/9×12/17=1/9×(7/15+12/17)=1/9×(7×17+12×15)/255=1/9×299/255=299/2295