Multiple choice

A boat goes $48\ km$ downstream in $20\ h$. It takes $4\ h$ more to cover the same distance against the stream. What is the speed of the boat in still water ?

  1. $2.2\ km/h$
  2. $2\ km/h$
  3. $4\ km/h$
  4. $4.2\ km/h$
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A Correct answer
Explanation

Downstream speed = 48/20 = 2.4 km/h. Upstream time = 20 + 4 = 24 h. Upstream speed = 48/24 = 2 km/h. Speed of boat = (Downstream + Upstream) / 2 = (2.4 + 2) / 2 = 2.2 km/h.

AI explanation

Using the formula for speed, the downstream speed is 48 km divided by 20 hours, which is 2.4 km/h. The upstream speed is 48 km divided by 24 hours, which gives 2 km/h. The speed of the boat in still water is the average of the downstream and upstream speeds, calculated as (2.4 plus 2) divided by 2. This equals 4.4 divided by 2, giving a speed of 2.2 km/h.

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