8/3*5-12/5*7+16/7*9-20/9*11+24/11*13
=1/3+1/5-1/5-1/7+1/7+1/9-1/9-1/11+1/11+1/13
=1/3+1/13
=16/39Why?求超详细过程8/（3*5）=1/3+1/512/（5*7）=1/5+1/716/（7*9）=1/7+1/920/（9*11）=1/9+1/1124/（11*13）=1/11+1/13