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52 Serious Incident Prevention

Prison Break Exercise

Let’s test the theory that our decisions can often benefit from the input
of others. Most of us think of ourselves as having excellent analytical abil-
ities. However, in workshop settings I have found that only about 1 in 20
people can correctly solve the exercise below when given 15 to 20 minutes
to complete it. Take a few minutes to work through the exercise to evaluate
your analytical ability and to determine if you could benefit from collabo-
ration with others.

Exercise
Four prisoners are planning a midnight prison break. Their objective will
be to cross over a nearby gorge as quickly as possible to distance them-
selves from the bloodhounds that will be in pursuit. A rope bridge spans the
gorge, and a flashlight will be required to cross the bridge. Furthermore,
the maximum capacity of the rope bridge is two people at a time. The pris-
oners have been able to obtain only one flashlight for the escape.
The physical conditioning of the prisoners varies significantly and
they estimate that the most athletic of the four can cross the bridge in 1
minute. (This prisoner is known as prisoner #1.) A second, less athletic
prisoner (prisoner #2) will require 2 minutes to cross, a third prisoner
(prisoner #5) will require 5 minutes, and the least mobile prisoner (pris-
oner #10) will require 10 minutes to cross the bridge.
Given that the group only has one flashlight that must be carried for vi-
sion when crossing the bridge and that the bridge will hold a maximum of
two people, determine the order in which prisoners should cross the bridge
to minimize the time requirements for all four prisoners to cross the gorge.
Use the worksheet below as a guideline for developing the optimum
solution.
Notes: (1) When two prisoners cross together the time for the two to
cross will be equal to the time required for the slowest of the two prison-
ers. For example, if prisoners 1 and 10 cross together, the time for both to
cross is 10 minutes. (2) The flashlight must be hand-carried back and forth
across the gorge—no tossing of the light or other trick solutions.

Prison Break Worksheet
Action Taken Minutes Cumulative
Required Minutes
Elapsed
______ & ________ cross bridge
_______ returns with flashlight
_______ & _______ cross bridge
_______ returns with flashlight
______ & _______ cross bridge