A student was performing an experiment in Chemistry lab. He took two beakers X and Y, and put equal quantities of a strong acid and a weaker acid. The concentration of weaker acid is the same in both the containers X and Y. He then replaced 4 litres of solution from X with weaker acid and the concentration of weaker acid became twice what it was initially. If he then replaced 8 litres of solution from Y with weaker acid, then what was the ratio of increase in final concentration from initial concentration of weaker acid in solution Y to the initial concentration from of weaker acid in solution Y?