The following question, there are three statements I, II and III. Read the question carefully and mark your answer according to which statements(s) is/are sufficient to the answer the question. Find the distance after which the speed of the of the stream changes. Statement I: A man rowing a boat in downstream and the speed of the boat in still water is four times the speed of the stream. Statement II: The speed of the stream is 2 kmph which is increased by 2 kmph after travelling some distance thereby reaching the destination earlier by 5 minutes. Statement III: Total distance covered by the boat is 25 km in downstream.?

Option 4 : All I, II and II

Let x be the speed of the boat and y be the speed of the stream

From statement I, II and III

Speed of the stream = 2 kmph

Then the speed of the boat = 4 × 2 = 8 kmph

Initial speed of downstream = 8 + 2 = 10 kmph

Let after travelling a distance of ‘d’, the speed of the stream increase to 2kmph

Then speed of the stream = 4 kmph

And speed of the boat in still water = 4 x 4 = 16 kmph

Now increased speed of boat downstream = 16 + 4 = 20 kmph

25/10 = d/10 + (25 - d)/20 + 5/60

⇒ 2.5 = (6d + 75 - 3d + 5)/60

⇒ 2.5 × 60 = 3d + 80

⇒ 150 - 80 = 3d

⇒ d = 70/3 = 23.33 km