1又1/2 + 2又1/3+3又1/4+4又1/5+5又1/6
= 1+1/2+2+1/3+3+1/4+4+1/5+5+1/6
= 1+2+3+4+5+1/2+(1/3+1/6)+1/4+1/5
= 15+1/2+1/2+1/4+1/5
= 16+9/20
= 16又9/20