Remember that solubility products are the threshold values for the concentration of component ions before precipitation occurs. As such, whenever precipitation occurs, concentrations of free ions follow Ksp = [ion]^a [ion]^b [ion]^c ....

Also remember that when we compare ion concentrations, we can think of ions as a sum of concentrations: total = free + those involved in salt 1 + those involved in salt 2 + ...
In order to do this correctly, your concentrations must be correctly adjusted for the final volume by simplifying multiplying the initial concentration by the dilution factor (initial / final volume) *your concentration should DECREASE whenever a dilution occurs

In this question, the concentration of chromate is equal to the Ksp and there is assumed to be no additional chromate in precipitate since it occurs just before the endpoint. However, the same cannot be said for chloride and silver and so each concentration must be evaluated carefully.