Final answer:
To find the speed of the current, we calculate the boat's speed in still water from the upstream and downstream speeds and then find the difference from the downstream speed. The speed of the current is 0.5 km/h, which does not match any of the provided options. so, option d is the correct answer.
Step-by-step explanation:
The student is asking how to find the speed of a river's current given the speed of a boat moving upstream and downstream. To solve this, we first convert the time taken to cover 1 km upstream and downstream to hours. For upstream, 25 minutes is ⅔ of an hour, and for downstream, 12 minutes is ⅕ of an hour. Therefore, the upstream speed is 4 km/h (1 km/(⅔ h)) and the downstream speed is 5 km/h (1 km/(⅕ h)).
The speed of the boat in still water (Vb) can be calculated using the average of upstream and downstream speeds: Vb = ½ (upstream speed + downstream speed) = ½ (4 + 5) km/h = 4.5 km/h. And the speed of the current (Vc) would then be the difference between the downstream speed and the boat's speed in still water: Vc = downstream speed - Vb = 5 km/h - 4.5 km/h = 0.5 km/h.
However, none of the options provided (2, 3, 4, or 5 km/h) match this answer. So, we need to inform the student that there might be an error in the options or the data provided.