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b. What is the expected time to the next block?
Answer: 10 minutes - how long since the last block
Bitcoin mining is a progress-free process, therefore the expected time to the next block is always ten minutes, regardless of how much time has passed (assuming that the difficulty matches the deployed hashrate).
I also think that you are either interpreting the question 1.c. very differently from me.
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a. What is the probability that Alice finds the next block?
Answer: Less than 50% (x < .5)
Bob?
Answer: Greater than 50% (1 - x)
b. What is the expected time to the next block?
Answer: 10 minutes - how long since the last block
c. What is the expected value of Alice's reward at the time the next block is found?
Answer: With Alice’s chance of getting the next block reward being less than 50%, the expected reward for Alice is zero.
What about Bob?
Answer: With Bob’s chance of winning the next block being greater than 50%, Bob’s expected reward at the time of the next block is found is R.