In (1+x)n, if n is even, then the middle term is (2n+1)th term.So, Coefficient of middle term in (1+x)20=C1020
In (1+x)n, if n is odd, then the middle term is {(\frac{n+1}{2})}^{th}&{(\frac{n+3}{2})}^{th} term.So, Sum of Coefficient of two middle terms in
(1+x)19=C919+C1019
So required ratio =C919+C1019C1020=C1020C1020=1