=1/3 ×(3/2×5+3/5×8+3/8×11+……+3/95×98)=1/3(1/2-1/5+1/5-1/8+1/银简扒8-1/11+……锋昌+1/95-1/98)=1/3(1/咐橘2-1/98)=1/3×48/98=8/49