Final Saline Concentration After Dilution

Consider a situation where a scientist is conducting an experiment that involves the use of a solution. The scientist starts with 500 mL of a 10% saline solution. To create a different concentration, the scientist decides to remove 100 mL of the original solution and replace it with distilled water. What is the final concentration of the saline solution after this operation?

Let the initial concentration be represented as $$C_1 = 10\%$$, the final volume after removal and addition be $$V_f = 500\, mL$$, the volume removed as $$V_r = 100\, mL$$, and the volume of distilled water added as $$V_a = 100\, mL$$.