The total time taken by a boat to cover (d + 320) km distance in down...
Let’s assume the speed of the boat in still water is B and the speed of the stream is C.
The total time taken by a boat to cover (d+320) km distance in downstream and (d-400) km distance in
upstream is ‘t’ hours.
The same boat can cover ‘d’ distance in still water in 38.4 hours.
The total time taken by the same boat to cover (d - 96) km distance in downstream and ‘d’ distance in upstream is (t + 18.5) hours.
Now put Eq.(ii) in the above equation.
If the speed of stream is 24 km/h.
C = 24
Now put the value of C in the Eq.(iv).
After solving the above equation, we will get B = −40.864865, 40.
Negative value of B is not possible. So B = 40 km/h
Now put the value of B in Eq.(ii).
d = 38.4B = 38.4 × 40 = 1536 km
Time taken by the same boat to cover (d+64) km distance downstream =
= 25 hours
Hence, option b is the correct answer.