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HW3_Solution09

# HW3_Solution09 - TELCOM 2120 Network Performance Fall 2009...

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TELCOM 2120: Network Performance Fall 200 9 Homework 3: Solution Problem 1 (10 point) An application service provider which host corporate web pages has collected data on the time between system crashes in hours on it's host machines that run Windows NT and those that run Linux. The data is shown below. System Number of Crashes Mean Standard Deviation Windows NT 977 120.10 194.2 Linux 510 62.7 25.2 At a 95% confidence level does the data support the theory that Linux is on average more stable and reliable than Windows Vista? Compare the mean time between crashes by constructing independent confidence intervals and comparing them. For any confidence interval: + X 2 / 1 α Z n σ α = 0.05, n = 977, X = 120.10, σ = 194.2 + X 2 / 05 . 0 1 Z n σ = 120.10 + 975 . 0 Z 977 194.2 where 975 . 0 Z = 1.96 = (107.92, 132.28) 95% C.I. for Linux: α = 0.05, n = 510, X = 62.7, σ = 25.2 + X 2 / 05 . 0 1 Z n σ = 62.7 + 975 . 0 Z 510 25.2 where 975 . 0 Z = 1.96 = (60.51, 64.89) Since the intervals do not overlap and the lower bound on mean of Windows Vista (107.92) is higher than the upper bound on mean of Linux (64.89), we can conclude that Windows Vista is more stable than Linux.

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