In the calculation of variance for optimistic and pessimistic activity duration estimates made at the 95 or

Question:

In the calculation of variance for optimistic and pessimistic activity duration estimates made at the 95 or 90 percent level, the denominator of the fraction that approximates the standard deviation of the time distribution changes from the traditional (b – a)/6 to (b – a)/3.3 for 95 percent and to (b – a)/2.6 for 90 percent. Where did the 3.3 and the 2.6 come from?

Distribution
The word "distribution" has several meanings in the financial world, most of them pertaining to the payment of assets from a fund, account, or individual security to an investor or beneficiary. Retirement account distributions are among the most...