Stats help needed with random variables?

Posted on 2016-03-12 13:48:00 in Statistics by ALLEN

A manufacturing project has five independent phases whose completion must be sequential. The time to complete each phase is a random variable. 

Phase: 
Set up tools- mean (hours) 20, Standard deviation (hours) 4 
Milling and machining- mean (hours) 10, Standard deviation (hours) 2 
Finishing and painting- mean (hours) 14, Standard deviation (hours) 3 
Packing and crafting- mean (hours) 6, Standard deviation (hours) 2 
Shipping- mean (hours) 48, Standard deviation (hours) 6 

Question: 
Find the expected completion time and the standard deviation of completion time. 

Thank you for your help in advance

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