Multiple choice

A river $2\ km$ wide is flows at the rate of $2\ km/h$. A boatman who can row a boat at a speed of $4\ km/h$ in still water, goes a distance of $2\ km$ upstream and then comes back. The time taken by him to complete his journey is

  1. $60\ min$
  2. $70\ min$
  3. $80\ min$
  4. $90\ min$
Reveal answer Fill a bubble to check yourself
C Correct answer
AI explanation

The upstream speed is the boat's speed minus the river speed (4 - 2 = 2 km/h), and the downstream speed is their sum (4 + 2 = 6 km/h). The total time for the 2 km upstream and 2 km downstream journey is (2/2) + (2/6) = 4/3 hours. Converting this to minutes gives 80 minutes.

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