Find the speed of a boat in still water if the boat goes 12 km/h along the stream and 4 km/h against the stream.

8 km/h

We know that,

Downstream speed = (x + y) km/h

Upstream speed = (x - y) km/h

Given,

Distance covered in downstream = 12 km/h

Distance covered in upstream = 4 km/h

Let the speed of the boat and stream be a km/h and b km/h respectively.

According to the above concept

= (a + b) = 12 km/h ....(1)

= (a - b) = 4 km/h ....(2)

Adding equations (1) and (2), we get

= 2a = 16

= a = 8 km/h