1/8+1/24+1/48+...+1/2400
=1/4(1/2+1/2*3+1/3*4+...+1/24*25)
=1/4(1-1/2+1/2-1/3+1/3-1/4+...+1/24-1/25)
=1/4(1-1/25)
=(1/4)(24/25)
=6/25