Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.

The bed of a river of width D is dry, so that you can walk across it. Two islands stick up out of the river bed -- one is directly downstream from the other, separated from the first by the same distance D.

Suppose that you walk at a speed of v. How long will it take to walk from A on the left bank to B on the right bank?

____________________
How long will it take to walk back, from B to A?
____________________
How long will it take to make the round trip?
____________________

Now, suppose you start on island X and walk to the other island, Y. How long will that take?

____________________
How long will it take to walk back, from Y to X?
____________________
How long will it take to make the round trip?
____________________

Plug in some numbers: suppose that D = 2 km, v = 1 m/s. What are the times required for the two round trips?

____________________  vs. _________________

Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.