C. 42 km/hr
Feedback Let the speed in still water = x km/hr. Takes 20 min. to row 12 km upstream ? speed of u/s = 36 km/hr. Also, time taken for us is 1/3 more than for ds.
distance covered in ds will be 1/3 more.
Hence distance covered by man for ds in 20 min. = 12 × (12/3) = 16km.
So speed of ds = 48 km/hr.
x + y = 48 and x – y = 36 ? x = 42 km/hr.