1/24+1/35+1/48+1/63+1/80=1/2*(1/4-1/6)+1/2*(1/5-1/7)+1/2*(1/6-1/8)+1/2*(1/7-1/9)+1/2*(1/8-1/10)=1/2*(1/4-1/10)+1/2(1/5-1/7)=1/8+1/10-1/14=9/40-1/14=63/280-20/280=43/280
