Multiple choice

In still water, a boat can cover a distance of 10 km at a speed of 5 km/h in a certain time interval, and during the same time interval, it can cover a distance of 8 km while moving upstream in a river. What is the speed of the river (in km/h)?

  1. 3

  2. 1.5

  3. 1

  4. 2
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Boat speed in still water (v) = 10 km / time. So time = 10/5 = 2 hours. Upstream speed = distance / time = 8 km / 2 hours = 4 km/h. Upstream speed = v - stream speed (s). 4 = 5 - s, so s = 1 km/h.

AI explanation

Using the formula time equals distance divided by speed, the time interval for the still water journey is 10 / 5 = 2 hours. The upstream speed required to cover 8 km in this same 2 hours is 8 / 2 = 4 km/h. Since upstream speed equals the boat speed minus the stream speed, the river speed is 5 - 4 = 1 km/h.

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