A boat cover a distance of 30 km downstream in 2 h while it takes 6 h to cover the same distance distance upstream. What is the speed of the boat (in km/h)?

Speed of boat downstream = Distance covered / Time taken
= 30/2 = 15 km/h
Now, speed of boat upstream = Distance covered / Time taken
= 30/6 = 5 km/h
Now, speed of boat = (Speed download + Speed upstream) / 2
= (15 + 5) / 2 = 10 km/h