Example:
Consider the problem of scheduling an operating room. From
past experience we have observed that the expected time required
for a single operation is 2.5 hours with a standard deviation
of 1 hour. We decide to schedule the time for an operation
so that there is a 90% chance that the operation will be finished
in the allotted time. The question is how much time to allow?
We assume the time required is a random variable with a normal
distribution.
The figure shows the definition of the distribution created
with the add-in. The moments are computed with user-defined
functions. The entry in cell H9 is the solution to the
problem. It holds the function:
RV_Inverse(RV14, 0.9)
The function returns the value of the random variable where
the cumulative distribution is 0.9. Allowing 3.78 hours for
an
operation provides
a 90%
chance that the operation will be complete.
When numerical procedures are not available, probabilities
are computed using tables that appear in many text books.
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