Multiple choice

A man rows a boat 4 km upstream in 30 minutes and returns in 20 minutes. What is the speed (in km/h) of the stream?

  1. 2

  2. 3

  3. 4

  4. 5

  5. 6
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A Correct answer
Explanation

Upstream speed = 4 km / 0.5 hr = 8 km/h. Downstream speed = 4 km / (1/3) hr = 12 km/h. Stream speed = (Downstream - Upstream) / 2 = (12 - 8) / 2 = 2 km/h.

AI explanation

The upstream speed is 4 km divided by 0.5 hours, which equals 8 km/h, and the downstream speed is 4 km divided by (20/60) hours, which equals 12 km/h. The speed of the stream is calculated as half the difference between the downstream and upstream speeds. Therefore, the speed is (12-8)/2, resulting in 2 km/h.

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