prob of getting 15 of 20 correct
= C(20,15) (1/2)^20 = 15504/1048576 = .014785..
So what is your conclusion?
You have a friend who claims to psychic. You don't believe this so you test your friend by flipping a coin 20 times and having him predict whether each flip is heads of tails. If you are right, and your friend is NOT psychic, then the probability of guessing correctly on each flip is .5. Your friend correctly guesses 15 out of the 20 flips.
What is the probability of your friend correctly guessing 15 or more out of 20 flips if he is NOT really psychic?
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1 answer