generate event with $6.75space p^2q$, $20space p^3q^2$, $3.9space pq$?

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Can we generate event with probabilities (a) $6.75space p^2q$, (b) $20space p^3q^2$, (c) $3.9space pq$? If yes, then how? If no, then why?




Here, in a coin toss, let P(occurring head)$=p=1-q$



I can easily generate events for $3space pq$(with three trials which is just $3space p^2q+3space pq^2$), $10space p^3q^2$ (with five trials) and $3space p^2q$ (with three trials), but could not find anything in these cases. Thanks for any help!







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  • 1




    See also this more general question that was inspired by this question.
    – joriki
    Jul 16 at 21:40















up vote
2
down vote

favorite













Can we generate event with probabilities (a) $6.75space p^2q$, (b) $20space p^3q^2$, (c) $3.9space pq$? If yes, then how? If no, then why?




Here, in a coin toss, let P(occurring head)$=p=1-q$



I can easily generate events for $3space pq$(with three trials which is just $3space p^2q+3space pq^2$), $10space p^3q^2$ (with five trials) and $3space p^2q$ (with three trials), but could not find anything in these cases. Thanks for any help!







share|cite|improve this question















  • 1




    See also this more general question that was inspired by this question.
    – joriki
    Jul 16 at 21:40













up vote
2
down vote

favorite









up vote
2
down vote

favorite












Can we generate event with probabilities (a) $6.75space p^2q$, (b) $20space p^3q^2$, (c) $3.9space pq$? If yes, then how? If no, then why?




Here, in a coin toss, let P(occurring head)$=p=1-q$



I can easily generate events for $3space pq$(with three trials which is just $3space p^2q+3space pq^2$), $10space p^3q^2$ (with five trials) and $3space p^2q$ (with three trials), but could not find anything in these cases. Thanks for any help!







share|cite|improve this question












Can we generate event with probabilities (a) $6.75space p^2q$, (b) $20space p^3q^2$, (c) $3.9space pq$? If yes, then how? If no, then why?




Here, in a coin toss, let P(occurring head)$=p=1-q$



I can easily generate events for $3space pq$(with three trials which is just $3space p^2q+3space pq^2$), $10space p^3q^2$ (with five trials) and $3space p^2q$ (with three trials), but could not find anything in these cases. Thanks for any help!









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asked Jul 15 at 18:24









Stat_prob_001

18710




18710







  • 1




    See also this more general question that was inspired by this question.
    – joriki
    Jul 16 at 21:40













  • 1




    See also this more general question that was inspired by this question.
    – joriki
    Jul 16 at 21:40








1




1




See also this more general question that was inspired by this question.
– joriki
Jul 16 at 21:40





See also this more general question that was inspired by this question.
– joriki
Jul 16 at 21:40











1 Answer
1






active

oldest

votes

















up vote
1
down vote



accepted










For (b), for $0le kle4$ choose $20binom4k$ patterns with $3+k$ heads and $2+(4-k)$ tails, and thus each with probability $p^3+kq^2+(4-k)$. This is possible because $binom93+kge20binom4k$ for all $k$. The sum of the probabilities is



$$
sum_k=0^420binom4kp^3+kq^2+(4-k)=20p^3q^2(p+q)^4=20p^3q^2;.
$$



You can't do the other two for general $p$. Consider $p$ the reciprocal of any odd prime. Then the denominator of any probability in any finite number of trials is always a power of that odd prime and can never contain a factor of $2$, whereas the denominators of the two probabilities in $(a)$ and $(c)$ do.



This of course assumes that you were implying that the problem should be solved with a finite number of trials. It's easy to achieve any desired probability with infinitely many trials.






share|cite|improve this answer























  • but the first calculation gives $10p^3q^2$
    – Stat_prob_001
    Jul 16 at 17:47










  • @Stat_prob_001: Sorry! I replaced it by a slightly more involved solution that works (unless I've made another mistake...).
    – joriki
    Jul 16 at 19:41











  • @Stat_prob_001: I posted and answered a more general form of this question here: math.stackexchange.com/questions/2853884.
    – joriki
    Jul 16 at 21:39










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1 Answer
1






active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes








up vote
1
down vote



accepted










For (b), for $0le kle4$ choose $20binom4k$ patterns with $3+k$ heads and $2+(4-k)$ tails, and thus each with probability $p^3+kq^2+(4-k)$. This is possible because $binom93+kge20binom4k$ for all $k$. The sum of the probabilities is



$$
sum_k=0^420binom4kp^3+kq^2+(4-k)=20p^3q^2(p+q)^4=20p^3q^2;.
$$



You can't do the other two for general $p$. Consider $p$ the reciprocal of any odd prime. Then the denominator of any probability in any finite number of trials is always a power of that odd prime and can never contain a factor of $2$, whereas the denominators of the two probabilities in $(a)$ and $(c)$ do.



This of course assumes that you were implying that the problem should be solved with a finite number of trials. It's easy to achieve any desired probability with infinitely many trials.






share|cite|improve this answer























  • but the first calculation gives $10p^3q^2$
    – Stat_prob_001
    Jul 16 at 17:47










  • @Stat_prob_001: Sorry! I replaced it by a slightly more involved solution that works (unless I've made another mistake...).
    – joriki
    Jul 16 at 19:41











  • @Stat_prob_001: I posted and answered a more general form of this question here: math.stackexchange.com/questions/2853884.
    – joriki
    Jul 16 at 21:39














up vote
1
down vote



accepted










For (b), for $0le kle4$ choose $20binom4k$ patterns with $3+k$ heads and $2+(4-k)$ tails, and thus each with probability $p^3+kq^2+(4-k)$. This is possible because $binom93+kge20binom4k$ for all $k$. The sum of the probabilities is



$$
sum_k=0^420binom4kp^3+kq^2+(4-k)=20p^3q^2(p+q)^4=20p^3q^2;.
$$



You can't do the other two for general $p$. Consider $p$ the reciprocal of any odd prime. Then the denominator of any probability in any finite number of trials is always a power of that odd prime and can never contain a factor of $2$, whereas the denominators of the two probabilities in $(a)$ and $(c)$ do.



This of course assumes that you were implying that the problem should be solved with a finite number of trials. It's easy to achieve any desired probability with infinitely many trials.






share|cite|improve this answer























  • but the first calculation gives $10p^3q^2$
    – Stat_prob_001
    Jul 16 at 17:47










  • @Stat_prob_001: Sorry! I replaced it by a slightly more involved solution that works (unless I've made another mistake...).
    – joriki
    Jul 16 at 19:41











  • @Stat_prob_001: I posted and answered a more general form of this question here: math.stackexchange.com/questions/2853884.
    – joriki
    Jul 16 at 21:39












up vote
1
down vote



accepted







up vote
1
down vote



accepted






For (b), for $0le kle4$ choose $20binom4k$ patterns with $3+k$ heads and $2+(4-k)$ tails, and thus each with probability $p^3+kq^2+(4-k)$. This is possible because $binom93+kge20binom4k$ for all $k$. The sum of the probabilities is



$$
sum_k=0^420binom4kp^3+kq^2+(4-k)=20p^3q^2(p+q)^4=20p^3q^2;.
$$



You can't do the other two for general $p$. Consider $p$ the reciprocal of any odd prime. Then the denominator of any probability in any finite number of trials is always a power of that odd prime and can never contain a factor of $2$, whereas the denominators of the two probabilities in $(a)$ and $(c)$ do.



This of course assumes that you were implying that the problem should be solved with a finite number of trials. It's easy to achieve any desired probability with infinitely many trials.






share|cite|improve this answer















For (b), for $0le kle4$ choose $20binom4k$ patterns with $3+k$ heads and $2+(4-k)$ tails, and thus each with probability $p^3+kq^2+(4-k)$. This is possible because $binom93+kge20binom4k$ for all $k$. The sum of the probabilities is



$$
sum_k=0^420binom4kp^3+kq^2+(4-k)=20p^3q^2(p+q)^4=20p^3q^2;.
$$



You can't do the other two for general $p$. Consider $p$ the reciprocal of any odd prime. Then the denominator of any probability in any finite number of trials is always a power of that odd prime and can never contain a factor of $2$, whereas the denominators of the two probabilities in $(a)$ and $(c)$ do.



This of course assumes that you were implying that the problem should be solved with a finite number of trials. It's easy to achieve any desired probability with infinitely many trials.







share|cite|improve this answer















share|cite|improve this answer



share|cite|improve this answer








edited Jul 16 at 19:41


























answered Jul 16 at 4:49









joriki

164k10180328




164k10180328











  • but the first calculation gives $10p^3q^2$
    – Stat_prob_001
    Jul 16 at 17:47










  • @Stat_prob_001: Sorry! I replaced it by a slightly more involved solution that works (unless I've made another mistake...).
    – joriki
    Jul 16 at 19:41











  • @Stat_prob_001: I posted and answered a more general form of this question here: math.stackexchange.com/questions/2853884.
    – joriki
    Jul 16 at 21:39
















  • but the first calculation gives $10p^3q^2$
    – Stat_prob_001
    Jul 16 at 17:47










  • @Stat_prob_001: Sorry! I replaced it by a slightly more involved solution that works (unless I've made another mistake...).
    – joriki
    Jul 16 at 19:41











  • @Stat_prob_001: I posted and answered a more general form of this question here: math.stackexchange.com/questions/2853884.
    – joriki
    Jul 16 at 21:39















but the first calculation gives $10p^3q^2$
– Stat_prob_001
Jul 16 at 17:47




but the first calculation gives $10p^3q^2$
– Stat_prob_001
Jul 16 at 17:47












@Stat_prob_001: Sorry! I replaced it by a slightly more involved solution that works (unless I've made another mistake...).
– joriki
Jul 16 at 19:41





@Stat_prob_001: Sorry! I replaced it by a slightly more involved solution that works (unless I've made another mistake...).
– joriki
Jul 16 at 19:41













@Stat_prob_001: I posted and answered a more general form of this question here: math.stackexchange.com/questions/2853884.
– joriki
Jul 16 at 21:39




@Stat_prob_001: I posted and answered a more general form of this question here: math.stackexchange.com/questions/2853884.
– joriki
Jul 16 at 21:39












 

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