Multiple choice

Upstream speed is 6 km/hr less than the downstream speed. The speed of the boat is 21 km/hr. Find the time (in hour) to cover the distance of 108 km in the upstream.

  1. 4

  2. 5

  3. 8

  4. 9

  5. 6
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Let boat speed = b, stream speed = s. Downstream speed = b + s, Upstream speed = b - s. Given: b - s = (b + s) - 6, so b - s = b + s - 6, giving 2s = 6, so s = 3 km/hr. Boat speed b = 21 km/hr. Upstream speed = 21 - 3 = 18 km/hr. Time for 108 km upstream = 108/18 = 6 hours. Option E is correct.

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