A boat travels upstream at the speed of 20 km/h and downstream at the speed of 30 km/h. What is the speed of the boat in still water?

25 km/h

Let speed of boat = B km/h

& Speed of Stream = S km/h

Speed of Downstream = ( B + S ) km/h

Speed of Upstream = ( B - S ) km/h

According to question ,

B + S = 30 km/h    -------(1)

B - S = 20 km/h    --------(2)

Adding equation 1 & 2

2B = 50 km/h

B = 25 km/h

So , Speed of Boat = 25 km/h