The percentage of ionisation of 1 L of $x \mathrm{M}$ acetic acid is 4.242 and is called solution " $A$ ". The percentage of ionisation of 1 L of $y \mathrm{M}$ acetic acid is 3 and is called solution " $B$ ". Solution " $A$ " is mixed with solution " $B$ ". What is the concentration of acetic acid in the resultant solution? ( $K_{\mathrm{a}}$ of acetic acid $=1.8 \times 10^{-5}$ )

At $25^{\circ} \mathrm{C}, K_a$ of formic acid is $1.8 \times 10^{-4}$. What is the $K_b$ of $\mathrm{HCOO}^{-}$?

At $25^{\circ} \mathrm{C}$, the percentage of ionisation of ' $x$ ' M acetic acid is 4.242 . What is the value of $x$ ? $\left(K_{\mathrm{a}}=1.8 \times 10^{-5}\right)$