Compute the mean and variance of each WP using the PERT formulas  . Cost estimates (Unit is $1,000). Work package Description Optimistic cost Most likely cost Pessimistic cost WP.1 Foundation 35 40 50 WP.2 Structure and roof 80 90 110 WP.3 Power, HVAC, etc. 38 40 45 WP.4 Interior 50 60 80 WP.5 Exterior 20 20 30 Sum 223 250 315.