NIFT UG 2015 Question Paper with solutions

Let, speed of ferry = u km/h
and speed of still water = v km/h
downstream speed, u + v = 45 km/hr
upstream speed, u – v = 30 km/hr
∴ u = 37.5 km/h and v = 7.5 km/h
Again, let speed of passenger in the river is x km/h.
From question,
$\frac{\mathit{d}}{45}+\frac{\mathit{d}}{30}=\frac{\mathit{d}}{2\left(\mathit{x}-7.5\right)}$
$\frac{5}{90}=\frac{1}{2\left(\mathit{x}-7.5\right)}$
$\mathit{x}-7.5=9$
$\mathit{x}=16.5$km/h
Hence, speed of passenger in the river = 16.5 km/h. None of the given options matched