Multiple choice

A boat running downstream covers a distance of $20\ km$ in $2$ hrs while it covers the same distance upstream in $5$ hrs. Then speed of the boat in still water is

  1. $7\ km/hr$
  2. $8\ km/hr$
  3. $9\ km/hr$
  4. $10\ km/hr$
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A Correct answer
Explanation

Downstream speed = 20/2 = 10 km/h. Upstream speed = 20/5 = 4 km/h. Boat speed = (10+4)/2 = 7 km/h.

AI explanation

The speed of the boat downstream is 20 km divided by 2 hrs equaling 10 km/hr, and its speed upstream is 20 km divided by 5 hrs equaling 4 km/hr. Using the still water speed formula, which is half the sum of the downstream and upstream speeds, we add 10 and 4 to get 14. Dividing 14 by 2 gives the speed of the boat in still water as 7 km/hr. The speed is 7 km/hr.

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