Question

Alex : Hey Bob, I think this coin is biased; I flipped it a few times and it always lends Tail. I think p, the probability of landing Head, must be less than 5%. Can you take a look?

Bob: Seriously? I bet it's fair, that is I think p = 1/2. Let me flip it three times and count the number of Heads. If the number of Heads is smaller than some threshold t, then I will buy you dinner. Otherwise, you will buy me dinner.
Alex: Wow Bob, okay! I will go ahead and reserve a fancy restaurant.
Bob: One last thing, though, just to make things fair: pick any t you want, but let's keep the proba- bility that I buy you dinner even if I'm right (that is, even if the truth is p= 1/2) below 10% please.
Alex: Go away, Bob! Stop wasting my time!
Question: why did Alex get mad?

Answer 1

See below

Explanation:

Alex finally understands how Bob was trying to trick him into winning the bet because of how he puts in the condition for probability being less than 10%. Whichever way the outcome of the coin toss turns out to be, it will be in Bob's favor and Alex will lose the bet. If the coin is flipped 3 times, the probability of having heads exactly twice is
`(4)/(9)`