1/3+1/6+1/12+1/24+1/48=（1/3+1/6+1/12+1/24+1/48+1/48）-1/48=（1/3+1/6+1/12+1/24+1/24）-1/48=（1/3+1/6+1/12+1/12）-1/48=（1/3+1/6+1/6）-1/48=（1/3+1/3）-1/48=2/3-1/48=31/48