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Math Help - 2 coins flip

  1. #1
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    2 coins flip

    If I flip two coins 100 times, is there a 50/50 probability of getting heads or tails. True or false?

    I know that if I flip two coins I will either get HH, TT, HT or TH.

    P(H) is 0.75 for each flip with two coins
    P(T) is 0.75 for each flip with two coins

    But these probabilities are out of the four possible combinations, and I need them to be out of two, i.e. heads or tails:

    So, what is the long term probability of getting either a heads or a tails in the long term? Well, I isn't it 0.5 for each? Because if I flip the coins 100 times and count up how many heads I get and how many tails I get, theoritcally, I should get half of them as heads and half as tails.

    Does this sound right?
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  2. #2
    Moo
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    Hello,

    Flipping two coins are independent events.

    So P(H \cap H)=P(HH)=P(H)P(H)=0.75^2

    Can you continue ? :P
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  3. #3
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    Quote Originally Posted by Moo View Post
    Hello,

    Flipping two coins are independent events.

    So P(H \cap H)=P(HH)=P(H)P(H)=0.75^2

    Can you continue ? :P
    Hi

    I'm a bit confused.

    P(H) on one of the coins is 0.5
    P(H) on the other is also 0.5

    independent events, multiply the probabilities giving 0.25 chance of getting a head on both.

    I think that is what you are saying.

    I think the question is about how many heads would I end up with and how many tails would I end up with after 100 flips.

    After 100 flips, there should be 50 heads and 50 tails on the one coin and the same on the other right? Giving 100 heads altogether and 100 tails altogether, in other words 50/50. or am I not understandng this right?
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  4. #4
    Moo
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    But you've been given : "P(H) is 0.75 for each flip with two coins"

    Well, i'm a bit lost too, sorry >_<
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  5. #5
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    Quote Originally Posted by Moo View Post
    But you've been given : "P(H) is 0.75 for each flip with two coins"

    Well, i'm a bit lost too, sorry >_<
    It's OK, thanks for trying!

    I get the bit you said, I just don't get the bit I said! Maybe I'm just confusing myself....
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  6. #6
    Bar0n janvdl's Avatar
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    Quote Originally Posted by Sweeties View Post
    I know that if I flip two coins I will either get HH, TT, HT or TH.

    P(H) is 0.75 for each flip with two coins
    P(T) is 0.75 for each flip with two coins
    Oh I get it. They want to get at least ONE head when you flip TWO coins.

    P(\Omega) = HH , TT , HT , TH

    Let A be the event that you get at least one head.

    P(A) = HH , HT , TH

    Same for tails.
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