Multiple choice

A boat covers a certain distance downstream in 3 hours, and it covers the same distance upstream in 5 hours. If the speed of the boat in still water is 8 km / hr, hen the speed of the stream is

  1. 1 km/hr

  2. 1.5 km/hr

  3. 2 km/hr

  4. 3 km/hr
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let boat speed be B=8 and stream speed be S. Downstream speed = B+S, upstream speed = B-S. Distance = (B+S)*3 = (B-S)*5. 3(8+S) = 5(8-S) => 24 + 3S = 40 - 5S => 8S = 16 => S = 2.

AI explanation

Using the Time, Speed and Distance formula, the distance covered is constant, so the speed of the boat downstream multiplied by 3 equals the speed upstream multiplied by 5. This gives the ratio of downstream speed to upstream speed as 5:3. Since the speed of the boat in still water is the average of these two speeds, we can deduce the speeds are 10 km/hr and 6 km/hr, making the speed of the stream half their difference, which is 2 km/hr.

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