The speed of a boat in still water is 18 km/h and the speed of the current is 6 km/h. In how much time (in hours) will the boat travel a distance of 90 km upstream and the same distance downstream?
Step 1 — Effective speeds:
Downstream \(= 18 + 6 = 24\) km/h; upstream \(= 18 - 6 = 12\) km/h.
Step 2 — Time for each leg:
\[T_{down} = \frac{90}{24} = \frac{15}{4}\ \text{h},\quad T_{up} = \frac{90}{12} = \frac{15}{2}\ \text{h}\]
Step 3 — Total time:
\[\frac{15}{4} + \frac{15}{2} = \frac{15 + 30}{4} = \frac{45}{4} = 11\tfrac{1}{4}\ \text{hours}\]
Therefore the total time is \(\mathbf{11\tfrac{1}{4}}\) hours.
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Important Questions from Boat and River
The speed of a ship in still water is 5 km/hr and the speed of the stream is 2 km/hr. Rohan rows to place at a distance of 21 km and comes back to the starting point. The total time taken by him is:
The speed of a boat in still water is 9 km/hr and the speed of stream is 3 km/hr. The difference between the upstream speed and downstream speed will be:
A boat can go 10 km upstream and 11 km downstream in a total time of 52 minutes, If the speed of the stream is 5 km/h, then what is the speed (in km/h) of the boat when going downstream?
The upstream speed of the boat is 40 km/hr and the speed of the boat in still water is 55 km/hr. What is the downstream speed of the boat?
A. 75 km/hr
B. 70 km/hr
C. 60 km/hr
D. 65 km/hrA boat moving upstream takes 8 hours 48 minutes to cover a distance while it takes 4 hours to return to the starting point, downstream. What is the ratio of the speed of boat in still water to that of water current?
