1. Check whether the following can be defined as a probability mass function, and explain why. 
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3. i. 12 ( ) x f x = for x = 0,1,2,3,4 
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5. ii. 50 3 1 ( ) + = x f x for x = 0,1,2,3,4,5 
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7. b. Given that x k f x 2 ( ) = is a probability mass function for a random variable that can take on the values x = 0,1,2,3, and 
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9. 4. Determine the value of k.