What is degree of dissociation of $CH_3COOH$ if, $\Lambda^\circ (CH_3COO^-) = 50\text{ S cm}^2\text{ mol}^{-1}$, $\Lambda^\circ (H^+) = 350\text{ S cm}^2\text{ mol}^{-1}$ and molar conductivity of $5 \times 10^{-2}\text{ M }CH_3COOH$ is $20\text{ S cm}^2\text{ mol}^{-1}$ ?