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Please find attached XLS that calculates the probability (using PERT). I am not entirely clear though between the "within" and "at least" calculation.

For right now, my calculations are based on "within". How should I modify the calculations to determine the probability for the "at least"?

Thank you,

EEH

PERT.xlsx

Please find attached XLS that calculates the probability (using PERT). I am not entirely clear though between the "within" and "at least" calculation.

For right now, my calculations are based on "within". How should I modify the calculations to determine the probability for the "at least"?

Thank you,

EEH

PERT.xlsx

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EXPERT OFFICE^{®} is a registered trademark of EXPERTS EXCHANGE^{®}

You have to convert the English to the correct range in months, and do the math.

PERT-2.xlsx

You can also use Excel for the latest problem as well.

The

You need to know the mean and the standard deviation (which is sqrt(81)=9 in this case).

The table doesn't help if you have fractions of a month, but the formula works just fine.

The cumulative version of the formula gives you the

within 20 months = 0.3415

within 25 months = 0.9488

At least 17 months means exactly the same thing as not within 16 months.

at least 17 months ==> not within 16 months = (1 - 0.0206)

at least 23 months ==> not within 22 months = (1 - 0.6568)

If you specify a single month . . . What is the probability that it will take 22 months

Then you probably mean more than 21 months, but not more than 22 months.

prob(22) - prob(21) = (0.6585 - 0.5000)

16.5 months is neither "at least 17 months", nor "within 16 months".

I did notice that the specification of the problem relied on integers, and that you were using the NORM.DIST function in Excel which uses real numbers.

The probability of any real-world mean of a real-number process being 12.000... is very small (zero).

Integers are often appropriate in legal and commercial transactions.

You can eat 16.5 apples, but you probably have to purchase 17.

The cost of airport parking is $20 per day or** any fraction there of**.

This is the method I was assuming.

From your second question:This is the method I was assuming.

>>

What does 52 weeks mean? How are you treating numbers? How do you want to treat numbers?

The probability that the project will be completed in exactly 52.000... weeks is zero.

The probability that it will be completed at

and the probability that it will be completed at

are close but not equal.

The probabilities for within 20 and within 25 are correct, as long as

ozo is correct.

You can make a case for

But it wouldn't hold up to a decimal point.

Interpret the question as best you can, then make a precise answer.

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