The ratio of the speed of boat to speed of the stream is 7 2 The taken by boat to cover 450 km dista...........

Quantitative Aptitude(IBPS CL) Boats and Streams

The ratio of the speed of boat to speed of the stream is 7 : 2. The taken by boat to cover 450 km distance upstream is 20 hours more than that to cover the same distance downstream. What is the difference between the upstream and downstream speed of the boat?

15 km/h

12 km/h

6 km/h

8 km/h

None of these

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Explanation:

Let the speed of the boat be 7x km/h.
Then, the speed of the stream = 2x km/h
According to the data provided in the question, we get:

⇒ 40 = 20x
⇒ x = 2
Speed of the boat in still water = 7 × 2 = 14 km/h
Speed of the stream = 2 × 2 = 4 km/h
Speed of the boat in upstream = 14 – 4 = 10 km/h
Speed of the boat in downstream = 14 + 4 = 18 km/h
Required difference = 18 – 10 = 8 km/h