Hydrochloric acid, c= 0,01 mol* dm^3, was diluted by adding the same volume of water. What is the pH of diluted acid?

Hydrochloric acid, c= 0,01 mol* dm^3, was diluted by adding the same volume of water. What is the pH of diluted acid?
correct answer is 2,30. Can anyone explain ? And what does it mean the same volume? I mean of what?
Thank you