Quick question on Solution Stoichiometry

I was doing a problem on limiting reagent when dealing with solutions and was wondering when one finds the limiting reagent, why it is incorrect to add the total volume together to find the moles of the reactants?

--------------------------------------------------------------------------------------------------------------
Example: A 25 mL sample of 1.20M KCl solution is mixed with 15 mL of 0.900M Ba(NO3)2 solution. BaCl2 is collected, dried and found to weigh 2.45 g. Find the limiting...

Quick question on Solution Stoichiometry