Consider the following first order completing reactions : $X\;\overset{k_1}{\longrightarrow}\;A+B$ and $Y\;\overset{k_2}{\longrightarrow}\;C+D$ if $50\%$ of the reaction of $X$ was completed when $87.5\%$ of the reaction of $Y$ was completed , the ratio of their constants $(k_1/k_2)$ is
