80又(1/7)*(7/8)+71又(1/6)*(6/7)+61又(1/5)*(5/6)+51又(1/4)*(4/5)+41又(1/3)*(3/4)=(561/7)*(7/8)+(427/6)*(6/7)+(306/5) *(5/6)+(205/4)*(4/5)+(124/3)*(3/4)=561/8+427/7+306/6+205/5+124/4=561/8+248/8+61+51+4...