\({{1} \over 3\times4} + {{1} \over 4\times5} + {{1} \over 5\times6} + ... + ...............{{1} \over 20\times21}\)On simplification, the given expression will give the result as:
1
\({{1} \over 20}\)
2
\({{2} \over 7}\)
3
\({{3} \over 7}\)
4
\({{1} \over 7}\)