Pert Analysis - Normal Probability Tables

Posted on 2009-02-19
Last Modified: 2012-05-06

I'm doing some work on PERT Analysis.  In the example that I've been given it says to multiply the standard deviation by a value from the normal probability table, in the example given it states 1.96 will give 2.5% chance of going over.

Ive looked at the normal probability table and cannot see how the figure 1.96 or 2.5% is created?

Can anybody explain how the percentage figure is derived from the value?

Question by:andyw27
    LVL 58

    Accepted Solution

    Look at the row 1.9, skid over to column 0.06, you will read 0.97500. This means that P(X<1.96) = 0.975, or 97.5%. Conversely, P(X>1.96) will be 0.025, or 2.5%. In plain English, if a variable X follows a normal distribution of mean 0, and standard deviation 1, each draw will have only a 2.5% probability of being over 1.96.

    Does that help?

    Author Comment

    Thanks thats a great answer.

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