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handout_4_3 - 4.3 Random Variables random variable a...

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4.3 Random Variables random variable - a variable whose value is a numerical outcome of a random phenomenon toss coin 4 times- could record outcome as string of heads and tails (HTTH) let X be number of heads- X=2 (X is random variable) Discrete random variable A discrete random variable X has a finite number of possible values. The probability distribution of X lists the values and their probabilities: Value of X x 1 x 2 x 3 … x k Probability p 1 p 2 p 3 … p k The probabilities p i must satisfy two requirements: 1. Every probability p i is a number between 0 and 1. 2. p 1 + p 2 + p 3 + …+ p k = 1 Find the probability of any event by adding the probabilities p i of the particular values x i that make up the event. EX Value of X 0 1 2 3 4 Probability 0.01 0.05 0.30 0.43 0.21 Choose a student at random. What is the probability they got a B or better (A=4)? P(X 3) = P (X=3) + P (X=4)= 0.64 Figure 4.5 - probability histograms

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EX What is the probability distribution of the discrete random variable X that counts the number of heads in four tosses of a coin?
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