20 mL of 2 M NaOH solution is added to 400 mL of 0.5 M NaOH solution. The final concentration of the solution is ____ × 10^-2 M. (Nearest integer)

$\displaystyle 20$ mL of $\displaystyle 2$ M NaOH solution is added to $\displaystyle 400$ mL of $\displaystyle 0.5$ M NaOH solution. The final concentration of the solution is $\displaystyle \_\_\_\_$ $\displaystyle \times 10^{-2} \mathrm{M}$. (Nearest integer)