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An unbiased coin is tossed 5 times. Suppose that a variable X is assigned the value k when k consecutive heads are obtained for k = 3, 4, 5, otherwise X takes the value –1. Then the expected value of X, is :

1. 16 3
2. 8 1 −
3. 8 1
4. 16 3 −

Correct answer: 8 1

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