Multiple choice

A man can row a boat in still water at the rate of 6 km per hour. If the stream flows at the rate of 2 km/hour, he takes half the time going downstream than going upstream the same distance. His average speed for upstream and down stream trip is -

  1. 6 km/hour

  2. 16/3 km/hour

  3. Insufficient data to arrive at the answer

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Boat speed (b) = 6, stream speed (s) = 2. Downstream speed = 6+2 = 8. Upstream speed = 6-2 = 4. Let distance be d. Time_down = d/8, Time_up = d/4. Average speed = Total Distance / Total Time = 2d / (d/8 + d/4) = 2d / (3d/8) = 16/3.

AI explanation

The speed of the man upstream is calculated as his speed in still water minus the speed of the stream, giving 6 km/hr minus 2 km/hr to equal 4 km/hr. His speed downstream is 6 km/hr plus 2 km/hr, which equals 8 km/hr. Using the formula for average speed for equal distances, 2 multiplied by upstream speed multiplied by downstream speed divided by their sum, we get 2 multiplied by 4 multiplied by 8 divided by 12. The average speed is 16/3 km/hr.

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