### Boats and Streams

The two quantities that come into the picture are the speed of the stream or river or current, and the speed of the boat or swimmer in still water.

- When the boat is moving against the current, it is said to move Then the effective speed at which it moves is the difference between its speed in still water and the speed of the current.
- When the boat is moving with the current, it is said to move Then the effective speed at which it moves is the sum of its speed in still water and the speed of the current.

If u and v are the upstream and downstream speeds of the boat, then

- Speed of the boat in still water = (
__u + v)/2__

- Speed of the stream = (v-u)/2