AP Police SI Exam Prelims 2018 Paper 1 (Mental Ability)

Two pipes can separately fill a tank in 20 hrs and 30 hrs respectively. Both these pipes are opened simultaneously and after the tank is $\frac{1}{3^{\mathit{r}\mathit{d}}}$ full, a leak develops in the tank through which $\frac{1}{3^{\mathit{r}\mathit{d}}}$ of water supplied thereafter by both pipes gets leaked out. The total time (in hours) taken to fill the tank is