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Thread: jblaze: coin toss

  1. #1
    jblaze
    Guest

    jblaze: coin toss

    I toss 2 coins, one lands heads up. What is the probability the other coin is heads up also?

  2. #2
    Don Schlesinger
    Guest

    Don Schlesinger: One-third

    > I toss 2 coins, one lands heads up. What is the
    > probability the other coin is heads up also?

    You have to be a little clearer with your statement. You probably don't mean, "I toss the first one and it's heads; what is the chance that the second one will also be heads," which, of course, is one-half.

    I sense that you mean, "I tossed two coins and at least one of them was a head. What is the chance that the other one was also a head?" In that case, the answer is one-third.

    There are four ways two coins can land, but when you announce "one lands heads up," you eliminate the tails-tails possibility. So three equiprobable results remain: H-H, H-T, and T-H. Only one of them makes "the other coin heads up also," so the answer is one chance out of three.

    Don

  3. #3
    jblaze
    Guest

    jblaze: Re: One-third

    OK, I'll come up with a more challenging question.

    > You have to be a little clearer with your statement.
    > You probably don't mean, "I toss the first one
    > and it's heads; what is the chance that the second one
    > will also be heads," which, of course, is
    > one-half.

    > I sense that you mean, "I tossed two coins and
    > at least one of them was a head. What is the chance
    > that the other one was also a head?" In that
    > case, the answer is one-third.

    > There are four ways two coins can land, but when you
    > announce "one lands heads up," you eliminate
    > the tails-tails possibility. So three equiprobable
    > results remain: H-H, H-T, and T-H. Only one of them
    > makes "the other coin heads up also," so the
    > answer is one chance out of three.

    > Don

  4. #4
    Mr. Lee
    Guest

    Mr. Lee: Re: coin toss

    > I toss 2 coins, one lands heads up. What is the
    > probability the other coin is heads up also?

    do they have that game in a casino?

  5. #5
    Bettie
    Guest

    Bettie: why not?

    I never thought I'd see War in a casino! Hell, it was one of the JOKE GAMES in the movie Vegas Vacation!

    Bettie

  6. #6
    Sun Runner
    Guest

    Sun Runner: What's next?

    Soon they'll have you simply picking a number between one and ten (I loved that part.)

    My all-time favorite casino game to date .. playing tic-tac-toe against a live chicken.

  7. #7
    jblaze
    Guest

    jblaze: OK how good are you at Bayes?

    what's the probability of a patient having cancer if the mammogram is negative, where, if the patient has cancer the mammogram will detect it 80% of the time and if the patient does not have cancer the mammogram will issue a false positive 10% of the time? The probability of cancer is 1%.

    > Soon they'll have you simply picking a number between
    > one and ten (I loved that part.)

    > My all-time favorite casino game to date .. playing
    > tic-tac-toe against a live chicken.

  8. #8
    MGP
    Guest

    MGP: Re: OK how good are you at Bayes?

    Hi,

    Last time I checked this was a blackjack forum and not a homework forum

    Good luck though,
    MGP

    > what's the probability of a patient having cancer if
    > the mammogram is negative, where, if the patient has
    > cancer the mammogram will detect it 80% of the time
    > and if the patient does not have cancer the mammogram
    > will issue a false positive 10% of the time? The
    > probability of cancer is 1%.

  9. #9
    Parker
    Guest

    Parker: Agreed

    Contrary to opinions posted on some websites, I am loath to delete posts without a compelling reason.

    However, I am scratching my head trying to find the blackjack content in this thread.

  10. #10
    jblaze
    Guest

    jblaze: Re: Agreed

    Grosjean also gives a couple examples of Bayes' Theorem in Beyond Counting. I thought some people might want to expand their knowledge beyond learning systems that gain percentages of mediocre systems to begin with or cracking jokes about Hooters.

    > Contrary to opinions posted on some websites, I am
    > loath to delete posts without a compelling reason.

    > However, I am scratching my head trying to find the
    > blackjack content in this thread.

  11. #11
    lagavulin62
    Guest

    lagavulin62: Re: Agreed

    > Grosjean also gives a couple examples of Bayes'
    > Theorem in Beyond Counting. I thought some people
    > might want to expand their knowledge beyond learning
    > systems that gain percentages of mediocre systems to
    > begin with or cracking jokes about Hooters.

    whatever happened to that guy who came in here a few weeks back with the intent to "wrestle control away" from the math studs? we could sure use his help about now.

  12. #12
    jblaze
    Guest

    jblaze: Soln. - warning, no BJ content

    p(cancer|neg) = p(neg|cancer)/[p(neg|cancer)p(cancer) + p(negative|benign)p(benign)]

    = (.2)(.01)/[(.2)(.01)+(.9)(.99)] = .0022.

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