Well, when you combine these to solutions, the initial (before any precipitation occurs, if it will) concentrations of Ag+ = 0.01 M and of Cl- = 0.0005 M. Multiply those two numbers together and compare them to the Ksp for AgCl. IF the product is greater than the Ksp for AgCl, precipitation will occur. If the product is less than the Ksp, then no precipitation will happen.