Multiple choice

A man can swim 5 km/hr in still water. If the velocity of the stream be 4 km/hr, the time taken by him to swim to a place 18 km upstream and back is -

  1. 16 hr.

  2. 20 hr.

  3. 24 hr.

  4. 18 hr.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Speed in still water = 5 km/hr, stream speed = 4 km/hr. Upstream speed = 5 - 4 = 1 km/hr. Downstream speed = 5 + 4 = 9 km/hr. Time to go 18 km upstream = 18/1 = 18 hours. Time to return 18 km downstream = 18/9 = 2 hours. Total time = 18 + 2 = 20 hours. This is a standard upstream-downstream time calculation.

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