Question

The total time taken by a boat travelling from X to Yand Y to Xis 2 hours. The speed of the boat is 12 kmph
and the distance between X and Y is 9 km. What is the speed of the current?​

Answer 1

The speed of the stream is 6 kmph

Given the distance between the two places be 9 km

Total time taken = 2 hours

let the Speed of current be a kmph

Speed of boat in still water is 12 kmph

when going upstream the speed would be 12-a kmph

Time taken to cover the distance  = 9/(12-a)

When going downstream the speed would be 12+a kmph

Time taken to cover distance would be 9/(12+a)

Total time taken would be :

9/(12-a) + 9/(12+ a) = 2 hrs

1/(12-a) + 1/(12+ a) = 2/9 hrs

12+a +12-a /(12-a) (12+ a) = 2/9

24/ 144 - a² = 2/9

12*9 =  144-a²

a² = 36

a = 6 kmph