Boats and Streams Quiz Set 014

Let v km/h be the rate of flow of the stream. Upstream and downstream times are equal. So $7/{95 - v}$ = $12/{95 + v}$. Solving for v, or verifying by putting the given options one by one, we get v = 25 km/h.

If the distance travelled is D, we have $D/{16/5 - R}$ = 3 × $D/{16/5 + R}$. Cancelling D, and solving for R, we get R = ${8/5}$, which is same as: $1{3/5}$ km/h.

The downstream speed is the speed along the direction of the flow of the stream. It is equal to the sum of the speed of the boat in still water and the speed of the stream. So the speed downstream is 5 + 2 = 7 km/h.

Speed of the boat in still water is the difference between its downstream speed and the speed of the stream, which is 28 - 12 = 16 km/h. Hence, the speed of the boat against the current is 16 - 12 = 4 km/h.

If the distance travelled is D and the speed of the current is R km/h, we have $D/{16/13 - R}$ = 3 × $D/{16/13 + R}$. Cancelling D, and solving for R, we get R = ${8/13}$ km/h. So downstream speed would be ${8/13}$ + $16/13$ = $1{11/13}$ km/h.