It took a crew 2 hours 40 minutes to row 6 km upstream and back again. If the rate of flow of the stream was 3 km/h, what was the rowing speed of the crew in still water?

1 Answer
May 30, 2018

Rowing speed in steel water is 66 km/ hour.

Explanation:

Let the rowing speed in steel water be xx km/ hour

Rowing speed in upstream is x-3x3 km/ hour

Rowing speed in downstream is x+3x+3 km/ hour

Total time taken is 22 hrs 4040 minutes i.e 2 2/3223hour

to cover up and down journey of 1212 Km

:. 6/(x-3) + 6/(x+3)=8/3 Multiplying by 3(x^2-9) on both

sides we get, 18(x+3) + 18(x-3)=8(x^2-9) or

8 x^2-36 x -72=0 or 2 x^2 - 9 x -18=0 or

2 x^2 - 12 x +3 x-18=0 or

2 x( x-6)+3(x-6)=0 or (2 x +3)(x-6)=0

:.x= 6 or x =-3/2 ; x != -3/2 :. x =6 km/hr

Rowing speed in steel water is 6 km/ hour [Ans]