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Math Help - Need help and some advice please check.

  1. #1
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    Need help and some advice please check.

    Hello! first I would like to say that Im from sweden and our math "lingo" might not be the same but I hope you will understand.
    the probability to get a 6 on a dice is 1/6 , but lets say I am about to throw the dice 3 times , what is the probability for me to get a 6 three times IN A ROW, the last part is really important, im not a math teacher but i think this is the correct answer:

    1/6* 1/6* 1/6= 1/216=0,0046296296296296296296296296296296 or
    ( dont know how to make that wavey equal sign thingy on the computer but I hope you understand) =0,5%

    my teacher says its like this 1/6 + 1/6 + 1/6 = 3/18 = 1/6 = 17% but I know that its incorrect , the probability for a person to get a 6 on the dice 3 times in a row cant possibly be 17% it just defies common sense! but I need to know if im correct and how do i explain this to my teacher ( my teacher is actually really good but he is from pakistan and is teaching in sweden so the communication might be kinda off but i would really appreciate if you would write mathematicly correct in english becouse i know that he understands english better than swedish.)

    and by the way do you guys got a good website for learning math? I got the highest grade in english so i would appreciate it if it was in english.( my swedish is actually worse than my english...) thanks for your time.

    and 1 more thing what do i write where the asterisk is in: P(*)
    if im going to calculate the probability for something lets say 3 times in a row , thank you once again!.
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  2. #2
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    You are correct.

    The chance of rolling exactly a 6 on a dice is 1/6. So to get a 6 three times in a row, your chances are (1/6) * (1/6) * (1/6) = 1/216.

    I took stats last year so I'll have to dig around for my notes on this, but I know there are situations in which you do add probabilities together like your teacher did, but not in this situation.

    I *THINK* what your teacher was thinking about is if you roll a dice three times, what is the probability that you will roll a 6 at least one of the times. In which case, you have (1/6) + (1/6) + (1/6) = 3/6 chance of rolling a 6 at least once.

    Your teachers math of (1/6) + (1/6) + (1/6) = 3/18 is wrong. When adding fractions with like denominators, you don't add the denominators together.
    Last edited by vesperka; October 8th 2007 at 01:04 PM.
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  3. #3
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by NiceBoy92 View Post
    Hello! first I would like to say that Im from sweden and our math "lingo" might not be the same but I hope you will understand.
    the probability to get a 6 on a dice is 1/6 , but lets say I am about to throw the dice 3 times , what is the probability for me to get a 6 three times IN A ROW, the last part is really important, im not a math teacher but i think this is the correct answer:

    1/6* 1/6* 1/6= 1/216=0,0046296296296296296296296296296296 or
    ( dont know how to make that wavey equal sign thingy on the computer but I hope you understand) =0,5%

    my teacher says its like this 1/6 + 1/6 + 1/6 = 3/18 = 1/6 = 17% but I know that its incorrect , the probability for a person to get a 6 on the dice 3 times in a row cant possibly be 17% it just defies common sense! but I need to know if im correct and how do i explain this to my teacher ( my teacher is actually really good but he is from pakistan and is teaching in sweden so the communication might be kinda off but i would really appreciate if you would write mathematicly correct in english becouse i know that he understands english better than swedish.)

    and by the way do you guys got a good website for learning math? I got the highest grade in english so i would appreciate it if it was in english.( my swedish is actually worse than my english...) thanks for your time.

    and 1 more thing what do i write where the asterisk is in: P(*)
    if im going to calculate the probability for something lets say 3 times in a row , thank you once again!.
    i doubt your teacher said that, i'm sure your teacher can at least add fractions!

    you are correct.

    1/6 + 1/6 + 1/6 = 3/6 = 1/2 is the answer to a different question: "what is the probability of rolling a 6 the first time OR the second time OR the third time?"

    the probability of rolling at least one 6 is (1 - probability of rolling no 6) = 1 - (5/6 * 5/6 * 5/6) = 91/216


    (and a word of caution, "common sense" does not always get you far when it comes to probability, think of "the birthday problem")
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  4. #4
    Grand Panjandrum
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    Quote Originally Posted by vesperka View Post

    I *THINK* what your teacher was thinking about is if you roll a dice three times, what is the probability that you will roll a 6 at least one of the times. In which case, you have (1/6) + (1/6) + (1/6) = 3/6 chance of rolling a 6 at least once.
    The probability of rolling a six on at least one of the dice is 1- the probaility
    of rolling no sixes = 1 - (5/6)^3 = 91/216 ~= 0.42

    RonL
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  5. #5
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    thanks alot guys! this really helped me alot , one of the difficulties for me to get a higher grade in math is that i cant really explain how im thinking but now i can explain to my teacher i thank you with all my heart!!!
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