So for a dilution, you want to use the dilution formula as shown below.

C_{1}V_{1}=C_{2}V_{2}

Where:

C

_{1} is the initial concentration

V

_{1} is the initial volume

C

_{2} is the desired concentration or final concentration

V

_{2} is the final volume needed to reach C

_{2}So in your scenario, the 1 molar solution of HCl is your C

_{1}. Your initial volume is how much of the HCl is going to be used. C

_{2} is the final concentration you want. Then you substitute the values into the equation and solve for V

_{2}, which is now the total volume needed to get to a concentration of C

_{2}.

Now to find how much water is needed to dilute HCl, you just do V

_{2} - V

_{1}. That would give you the amount of water needed to reach C

_{2} from the original volume.

Hope that helps.

Please correct me if I have done anything wrong.