September "Bravos" to Steve Weimar, Sarah Seastone, and Sum96 for the suggestions and examples, and Mike Morton for the nifty Applet.

Traffic Jam

Activity of the Month

September 1996

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Each month the Math Forum sponsors a student activity that can be done locally and shared globally. There are:

Traffic Jam

Traffic Jam is a game for any number of people, but it's probably best begun with an even number and 1, 2, or 3 on each side.

How to Play

Players divide into two groups and line up facing each other with one open slot in the middle:

1 2 3 ->     <- 4 5 6

The two groups exchange places, observing the following constraints:

  1. If the slot immediately in front of or behind you is empty, you may step into it. There is always only one slot empty.

  2. If there's a space on the other side of a person next to you, you may step around that person (but only around one person) into the space.

Object of the game:

1 2 3    4 5 6


4 5 6   1 2 3


Discussion suggestions:

  1. What's the minimum number of moves necessary for two people on a side? for three people on a side?
  2. How is this minimum number of moves related to the number of people on a side?
  3. What formula can account for the minimum number of moves for any number of people on a side?
  4. Is there a pattern in the different kinds of moves people make - for instance when they move directly into an empty slot and when they move around another player?
  5. Do you find a pattern related to the number of people on a side?
  6. Is there a simple set of directions a group can follow to accomplish the task in the minimum number of moves?

Examples of approaches to the activity.


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