9/20=1/4+1/510/21=1/3+1/711/24=1/3+1/812/35=1/5+1/71/3+3/4+2/5+5/7+7/8+9/20+10/21+11/24+12/35 =1/3+3/4+2/5+5/7+7/8+1/4+1/5+1/3+1/7+1/3+1/8+1/5+1/7=(1/3+1/3+1/3)+(3/4+1/4)+(2/5+1/5+1/5)+(5/7+1/7+1/7)+(...