Unformatted text preview: X ]. b. Find the second moment E [ X 2 ]. c. Find the variance var[ X ]. d. Find the standard deviation σ . 5. (2 pts) The probability that a telephone call lasts no more that t minutes is often modeled using the following exponential CDF: F T ( t ) = ( 1et 3 t ≥ otherwise Find the probability that a call duration is within ± 1 standard deviation of the expected call duration? (Hint: if E [ T ] is the expected value of t and σ is the standard deviation of t , ±nd the probability P [ E [ T ]σ ≤ t ≤ E [ T ] + σ ].) 1...
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 Fall '08
 GELFAND
 Variance, Probability theory, probability density function, Poisson random variable

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