2又3分之1+4又15分之1+6又35分之1+8又63分之1
=2+1/3+4+1/15+6+1/35+8+1/63
=2+4+6+8+1/3+1/15+1/35+1/63
=20+(2/3+2/15+2/35+2/63)/2
=20+[(1-1/3)+(1/3-1/5)+(1/5-1/7)+(1/7-1/9)]
=20+(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9)
=20+1-1/9
=20+8/9
=20又8/9
或188/9