4/15+4/35+4/63+4/99+4/11=2×(2/15+2/35+2/63+2/99)+4/11=2×(1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11)+4/11=2×(1/3-1/11)+4/11=2/3-2/11+4/11=2/3+2/11=22/33+6/33=28/33