Unformatted text preview: finished, what are the expected value and variance of the time required from beginning of excavation to completion of the foundation? You may assume that the two activities are independent. Answer: Let T be total time, X be excavation, C be construct foundation T = E + C Mean: E(T) = E(X) + E(C) = 120 + 200 = 320 hours Variance: σT2 = σX2 + σC2 = 202 + 452 = 2425 hours 2) Accidents at a busy Chicago intersection (#1) occur with an average rate of five times per year. At a neighboring intersection (#2), the average rate is three times per year. Accident frequencies at the two intersections are correlated (ρ = 0.4), because they are more likely when traffic is bad. As a transportation planner, you are interested in the total accidents at these two intersections. a) How many accidents are expected at these two intersections during six months? b) What is the s...
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 Spring '08
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