Question

The speed of a boat in still water is 15 km/h. It takes 4 & 1/2 hours to travel 30 km down the stream. Find the speed of the stream.​

Answer 1

Answer:

According to the given information, Time taken for upstream + Time taken for downstream = 4 (1/2) hours. ⇒ x = 5. Therefore, Speed of the stream = 5 km/hr...

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Answer 2

Answer:

Let the speed of the stream be x km/hr

Then,

Speed downstream = (15 + x) km/hr

Speed upstream = (15 - x) km/hr

$$\eqalign{ & \therefore \frac{{30}}{{ {15 + x} }} + \frac{{30}}{{ {15 - x} }} = 4\frac{1}{2} \cr & \Rightarrow \frac{{900}}{{225 - {x^2}}} = \frac{9}{2} \cr & \Rightarrow 9{x^2} = 225 \cr & \Rightarrow {x^2} = 25 \cr & \Rightarrow x = 5\,km/hr \cr} $$