title: 分数简算1/2*3+2/3*5+4/5*9+3/9*12+5/1 
desc: 1/2*3+2/3*5+4/5*9+3/9*12+5/12*17
answer: 1/(2*3)+2/(3*5)+4/(5*9)+3/(9*12)+5/(12*17)
  =(3-2)/(2•3)+(5-3)/(3•5)+(9-5)/(5•9)+(12-9)/(9•12)+(17-12)/(12•17)
  =(1/2-1/3)+(1/3-1/5)+(1/5-1/9)+(1/9-1/12)+(1/12-1/17)
  =1/2-1/17
  =15/34