1/2+1/3+2/3+1/4+2/4+3/4+...+1/50+2/50+...+49/501/2=1×1/21/3+2/3=1=2×1/21/4+2/4+3/4=6/4=3×1/2......1/50+2/50+...+49/50=49×1/2原式=(1+2+3+...49)×1/2=(1+49)×49÷2÷2=612.5
612.5