Stat 21 Quiz _3 Key

X px wins3 153604167 loses1 15364167

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Unformatted text preview: a commuter leaves her house at 8am each morning of a 5‐day work week, and each commute time is independent from all the others, what is the chance she will arrive to work by 8:40am on 3 of those days? True. P = .27 K=3 N=5 5! / 3! (5-3)! * .27^3 (1-.27)^2 = .105 Stat 21 Quiz #3 October 12, 2011 Name______________________________________________ Section # ___________________________________________ VERSION D 1. X is a random variable defined as: x ‐1 0 1 P(x) .20 .35 .45 A) Draw the cumulative distribution function (cdf) for X. B) Evaluate: i) P(X ≥ 1.8) = 0 ii) P(X ≤ ‐2.3) = 0 iii) P(X ≥ 0.5) = 0.45 D) Calculate: i) E(X) = 0.25 X ‐1 0 1 E(x) = Var(X) = P(X=x) 0.2 0.35 0.45 0.25 0.5875 ii) Var(X) = 0.5875 x ‐ u ‐1.25 ‐0.25 0.75 (x ‐ u)^2 1.5625 0.0625 0.5625 (x ‐ u)^2 * P(X=x) 0.3125 0.021875 0.253125 Stat 21 Quiz #3 October 12, 2011 2. Francie is playing a dice game with another GSI. In the game, she rolls a dice two times. If the second roll is bigger than the first, she wins $3. If the second roll is less than first, she loses $1. If the second roll is equal to the first roll she wins no money, but does not lose money. A) Create a probability model for the amount of money that Francie wins in the dice game. x P(x) Wins $3 15/36 = 0.4167 Loses $1 15/36 = .4167 No wins or losses (if two rolls are the same) 6/36 = .167 B) Draw a cumulative distribution function...
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This document was uploaded on 03/12/2014 for the course STAT 21 at Berkeley.

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