4/3+16/15+36/35+...+399%

=1+1/3+1+1/15+1+1/35+……+1+1/399

=10+(1/3+1/15+1/35+……+1/399)

=10+1/2×(1-1/3+1/3-1/5+1/5-1/7+……+1/19-1/21)

=10+1/2×(1-1/21)

=10+1/2×20/21

=10+10/21

=10 10/21