Speed of the boat along the current and against the current are 10 km/h and 8 km/h respectively. What is the speed of the current?

1

Let speed of current be 's'

Let speed of boat in still warter be 'b'

Speed of boat upstream  = 8 km/hr = b-s

Speed of boat downstream  = 10 km/hr = b+s

Adding both equations above, we get

2b = 18

b = 9

Thus s = 1

The correct answer is Option (4) → 1