Management Aptitude Test 2015 Paper

(d) Let the capacity of the tank be x L.
Time taken to fill a tank by pipe A = 20 min
Time taken to fill a tank by pipe B = 30 min
Time taken to empty a tank by pipe C = 45 min
= $\frac{\mathit{x}}{20}+\frac{\mathit{x}}{30}-\frac{\mathit{x}}{45}$
= $\frac{\left(9+6-4\right)}{180}\mathit{x}=\frac{11}{180}\mathit{x}$
Part emptied by C in 30 min
= $\frac{\mathit{x}}{45}\times 30=\frac{2}{3}\mathit{x}$
∴ Time taken to fill the tank
= $\frac{180}{11\mathit{x}}\times \frac{2\mathit{x}}{3}=\frac{120}{11}$
= 10.99 min