Calculate the pH of the solution when 25 mL of 0.10 M HCl is added to 25 mL of 0.050 M NaOH.

Look at the other problem I gave you. In this case, you won't have equal amounts of hydrogen ion and hydroxide ion so you have to calculate the concentration of hydrogen ion or hydroxide ion. Use the relation

[H^+][OH^-] = 10^{-14}