Multiple choice

A boat takes two hours to travels $8\ km$ and back in still water. If the velocity of water is $4\ km/h$, the time taken for going upstream $8\ km$ and coming back is

  1. $2\ hr$
  2. $2\ hr\ 40\ min$
  3. $1\ hr\ 20\ min$
  4. $2\ hr\ 30\ min$
Reveal answer Fill a bubble to check yourself
B Correct answer
AI explanation

The boat travels 8 km and back in 2 hours in still water, making its still water speed 8 km/h. Using the upstream and downstream speed formulas, the speeds against and with the 4 km/h current are 4 km/h and 12 km/h, respectively. The total time to travel 8 km upstream and 8 km downstream is the sum of their individual times: (8/4) + (8/12) hours, which equals 2 + 2/3 hours or 2 hours and 40 minutes. The result is 2 hr 40 min.

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