How do you calculate the pH of two acids in a solution? Examlp: a solution is made by adding 50mL acetic acid(Ka=1.76x10-5) to 50mL 1.00x10-3M HCl. What is the Ph of the solution?

There is no set formula for this because you can have all kinds of acids together. In this particular case you have HCl (a strong acid that ionizes 100%) and acetic acid (a weak acid that ionizes only about 1%). Also, the strong acid represses the ionization of acetic acid even more. The total H^+ will be the sum of the two; however, one can't calculate the H^+ from acetic acid until you furnish the concn of the acetic acid.