A motorboat goes 24 km in 2 hours along the stream and 10 km in 1 hour against the stream. The speed of the motorboat in kilometres per hour is:

11

Let the speed of the boat = x and the speed of the stream = y

Boat covers 24 km in 2 hours

In one hour = 12 km distance covered downstream

Upstream speed = 10 km per hour

According to the concept =

Downstream =

x + y = 12----(A)

upstream =

x - y = 10----(B)

From A and B we get,

x = 11 and y = 1

So the speed of the boat = 11