Hi Sara, this is a great question. There are two instances when you would take 1-Z... 1) When the expected completion time (the critical path) is LONGER than the specified time, and 2) When the expected completion time (the critical path) is shorter than the specified time, but the question asks "what is the probability it will take MORE THAN the specified time". The 2nd one is a little bit of a trick question. My students hate it. But that's the second example of when you would take 1-Z.
@@OperationsAndSupplyChain Thanks sooo much for answering my question, just to see if i got it if our critical path is 25 days and it asks to Determine the probability that the project will take more than 20 days to complete. and the standard dev is lets say 3... after finding the z and going to the table, thats when I do 1-Z but if my critical path (expected time) is 18 days, which is less than the specified date..... after finding the Z, there is no need to subtract by 1?
Correct. Assuming the question in the second statement is something like "if the critical path/expected time is 18 days and the project needs to be completed in 20 days, then what is the probability the project will be completed on time?".... Then you do not subtract by 1. You've got this!
