Quantitative Aptitude Ques 2278

Question: A boat running downstream covers a distance of 30 km in 2 h. While coming back the boat takes 6 h to cover the same distance. If the speed of the current is half that of the boat, what is the speed of that boat?

[IBPS (Office Assistant) 2015]

Options:

A) 15 km/h

B) 5 km/h

C) 10 km/h

D) 20 km/h

E) None of these

Show Answer

Answer:

Correct Answer: B

Solution:

  • Speed of boat = x Speed of stream = y Speed downstream $ =x+y $ We know that, $ Speed=\frac{Distance}{Time} $ Boat covers 30 km in 2 h in downstream Speed of boat downstream $ =\frac{30}{2}=15,km/h $ … (i) Speed of current (stream) $ =\frac{1}{2}th $ speed of boat $ y=\frac{1}{2}x $

$ \Rightarrow $ $ x=2y $ … (ii) Speed downstream $ =x+y $ $ 15=y+2y $

$ \Rightarrow $ $ 3y=15 $
$ \Rightarrow $ $ y=5km/h $ Speed of stream $ =,5,km/h $ Speed of boat $ =10,km/h $ Speed upstream $ =x-y=10-5=5,km/h $

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