A boat goes 20 km upstream in 2 hours and downstream in 1 hour. How much time this boat will take to travel 30 km in all still water?

A) 1 hr

B) 2 hrs

C) 1.5 hrs

D) 2.5 hrs

Correct answer:
B) 2 hrs

Description for Correct answer:

Let \( \Large v_{1} \) be the speed of boat in still water and \( \Large v_{2} \) be the speed of current

Therefore, \( \Large v_{1} \) + \( \Large v_{2} \) = 20 ...(i)

\( \Large v_{1} \) - \( \Large v_{2} = \frac{20}{2} \) = 10 ...(ii)

From equations (i) and (ii) we get

\( \Large v_{1} \) = 15 km/hr

\( \Large t = \frac{d}{v_{1}} = \frac{30}{15} = 2 hrs. \)



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