Boats and Streams Quiz Set 011

Speed of the boat in still water is the difference between its downstream speed and the speed of the stream, which is 18 - 4 = 14 km/h. Hence, the speed of the boat against the current is 14 - 4 = 10 km/h.

Let the speed of the boat in still water be u and the speed of the stream be v. The three speeds are u - v, u and u + v. They are in an A.P. with a common difference equal to v, and u as its middle term. Since u is also the speed of the boat in still water, the required answer is: $1{1/8}$.

By the shortcut method, the speed of the boat in still water is average of downstream and upstream speeds. So the required speed = ${6 + 4}/2$ = 5 km/h.

The downstream speed is the speed along the direction of the flow of the stream. It is equal to the sum of the speed of the boat in still water and the speed of the stream. So the speed downstream is 4 + 3 = 7 km/h.

Speed of the boat in still water is the difference between its downstream speed and the speed of the stream, which is 24 - 8 = 16 km/h. Hence, the speed of the boat against the current is 16 - 8 = 8 km/h.