Multiple choice

Speed of boat in still water is $5\ \text{ km/h}$. The river is flowing with a speed of $2\ \text{km/h}$ and time taken to cover a certain distance upstream is $2$ h more than time taken to cover the same distance downstream. Find the distance.

  1. $10.5\ \text{ km}$
  2. $11\ \text{km}$
  3. $10.9\ \text{km}$
  4. $15\ \text{km}$
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A Correct answer
Explanation

Let distance be D. Upstream speed = 5-2 = 3 km/hr. Downstream speed = 5+2 = 7 km/hr. D/3 - D/7 = 2. (7D - 3D) / 21 = 2. 4D = 42, so D = 10.5 km.

AI explanation

Let the required distance be d kilometers. The upstream speed is 5 minus 2, which is 3 km/h, and the downstream speed is 5 plus 2, which is 7 km/h. Using the given time difference, we set up the equation (d divided by 3) minus (d divided by 7) equals 2. Solving this equation gives 4d divided by 21 equals 2, so d equals 10.5 km.

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