Question

Speed of a boat in still water is 15 km/h. It goes 30 km upstream and returns

back at the same point in 4 hours 30 minutes. Find the speed of the stream
​

Answer 1

Answer:

50.5km/hr

Thanks

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Answer 2

GIVEN :-

• Speed of boat in still water = 15 km/h

• Distance travelled = 30 km

• Time taken = 4 hour 30 min = 4 + $\sf\dfrac{30}{60}$  = $\sf 4 \dfrac{1}{2}$

TO FIND :-

• Speed of the stream .

SOLUTION :-

 Let speed of the stream be x .

 Speed of the stream in upstream = ( 15 - x ) km/h

 Speed of the stream in downstream = ( 15 + x ) km/h

 By given ,

  Time = Distance / speed

  $\longrightarrow\sf \dfrac{30}{15+x} + \dfrac{30}{15-x} = 4 \dfrac{1}{2} \\\\\longrightarrow \dfrac{30(15-x) +30(15+x)}{(15+x)(15-x)} =\dfrac{9}{2}\\\\\longrightarrow \dfrac{450-30x+450+30x}{225 -x^2}=\dfrac{9}{2}\\\\\longrightarrow \dfrac{900}{225-x^2} =\dfrac{9}{2} \\\\\longrightarrow \dfrac{100}{225-x^2} = \dfrac{1}{2} \\\\\longrightarrow 225-x^2 = 200 \\\\\longrightarrow x^2 = 25 \\\\\longrightarrow x = 5$

Speed of the stream = 5 km/h