Question

A man rows a boat at a speed of 15 mph in still water. Find the speed of the river if it takes her 4 hours 30
minutes to row a boat to a place 30 miles away and return

Answer 1

Let the speed of the river = x mph

Speed of boat on outward journey = (15 – x) mph (Assuming the outward journey is upstream)

Speed on boat on return journey = (15 + x) mph

Time = Distance/Speed

4 hours 30 minutes = 4.5 hours

Total time taken = 30/(15 – x) + 30/(15 + x) = 4.5

       30(15 + x) + 30(15 - x)

     ___________________           = 4.5         

          (15 – x)(15 + x)

450 + 30x + 450 – 30x = 4.5(225 – x^2)

900 = 4.5(225 – x^2)

200 = 225 – x^2

x^2 = 25

x = 5

So, the speed of the river = 25

I hope it will help u

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