Probability and Statistics question

[mkamalkayani]

Please can anyone tell me what is optimistic cost and what is pessimistic cost. You may suggest a book or a link where I can find explanation. I have tried to search for it but could not find anything useful. I want to solve the questions shown below.
I will be grateful to you for your help. Thanks
View attachment 4887

 

[mkamalkayani]

This is how I tackle this problem.

Minimum possible cost is 301 million and the maximum possible cost is $340 million.
The difference between these costs is 39 million. The mean cost which exceeds from 325 is 340 million minus 325 million which is equal to 15 million.

Therefore, the probability that the future project mean cost will exceed 325 million is equal to 15/39 = 0.385 = 38.5%