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2Coins probability of Heads-tails in 40 tosses? HELP!

  1. Mar 25, 2005 #1
    2 coins are tossed at the same time There are 3 colums in a chart

    1) Heads-Heads
    2) Heads-Tails or Tails-Heads

    the coins were tossed 40 times simultaneously.

    What was the probability that heads-tails (or tails-heads) would appear? Show calculations.

    (HINT: The probability of these two combinations must be added together because they were recorded together.)

    Im thinking its 2/4 but not sure, and dont know what to show as calculations.
    PLEASE HELP ME! :redface:
  2. jcsd
  3. Mar 25, 2005 #2
    but im not so great with it either, but wouldnt it be 1/3 chance for all?
  4. Mar 25, 2005 #3
    For your information all of my posts are different questions so mind your own business.
  5. Mar 26, 2005 #4


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    Yes, you're correct.

    You have a 50% chance of coin 1 coming up heads. If coin 1 comes up heads, you have a 50% chance of coin 2 coming up heads. .5 * .5 gives you a 25% chance of both coins coming up heads.

    If you do the same for each combination, you wind up with a 25% chance of each combination coming up. Since the coins are tossed simultaneously, you don't know if you have heads-tails or tails-heads. So you add the probabilities for both combinations together.
  6. Mar 26, 2005 #5


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    Staff: Mentor

    Unless, of course, you have two different coins (say a quarter and a loonie) and it matters which one is which. Then you would consider loonie-heads and quarter-tails as a different outcome from loonie-tails and quarter-heads, each with 25% probability.
  7. Mar 26, 2005 #6
    can u show me what the calculation would look like BOB? I understand what your saying but not 100% sure.
  8. Mar 26, 2005 #7


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    Science Advisor
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    If this pertains to statistics, you'll need to employ proper formulas and concepts to solve this equation, it may NOT be 1/2.
  9. Mar 26, 2005 #8
    no this is not physics it was just a Bio lab using a little bit of probability to help understand mendel and the pea plant .
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