Infinite developers for the price of 3

Question : In a company XYZ Software International, one of the most senior and competent developers was given a task of building a new Team. For whatever reason or to keep the senior members aside for productive work, the manager sets a policy that the most recently recruited developer will conduct the subsequent interview. Assuming that a developer can ascertain only 60% of his own competency, how many developers should be recruited before the team will have an equivalent capability of 3 times the original developer. Consider the worst case scenario.

Solution : Never.
X + 0.6 X + 0.6^2 X + 0.6^3 X + ....till infinite = [ X / (1-0.6) ] = 2.5 X