Multiple choice

A motor ship covers the distance of 300 km between two localities on a river in 10 hrs downstream and in 12 hrs upstream. Find the flow velocity of the river assuming that these velocities are constant.

  1. 2.0 km/hr

  2. 2.5 km/hr

  3. 3 km/hr

  4. 3.5 km/hr
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Downstream speed (v+u) = 300/10 = 30 km/hr. Upstream speed (v-u) = 300/12 = 25 km/hr. Subtracting the two: (v+u) - (v-u) = 30 - 25 => 2u = 5 => u = 2.5 km/hr.

AI explanation

The downstream speed of the ship is the total distance divided by the time taken, which is 300 km divided by 10 hrs, yielding 30 km/hr. The upstream speed is calculated similarly as 300 km divided by 12 hrs, resulting in 25 km/hr. Using the relation that the river velocity is half the difference of the downstream and upstream speeds, we get (30 minus 25) divided by 2. The flow velocity of the river is 2.5 km/hr. The result is 2.5 km/hr.

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