How can i find the mean and standard deviation (probability) for PERT questions?

Question

If the normal distribution were used to find the probability of finishing this project in 24 weeks or fewer, what mean and standard deviation would be used?

(a) 20.833 and 5.144
(b) 22.167 and 5.144
(c) 23.2 and 2.362
(d) 20 and 4.222
(e) 23.2 and 1.537

 

Variance= 2.362

critical path= 23.1 

specified time= 24 

 

Note: I know the answer, but i don't know what is the process? so, please i want someone to explain. 

Answer 1

I took Statistics in Spring 2013, so it's been a while, but I believe Variance = Standard deviation^2. Here, the square root of the variance is 1.537, which brought me to E.

 

I'm wondering if you're taking it from more of a project management perspective. I just skimmed my notes on normal distribution and I don't have a single problem/spreadsheet/anything where you have to find the mean based on such little information. Based on my notes, I was always given something like a data table or probability in order to determine mean. Sorry I couldn't be more helpful on this part of the question. :(