20 blue balls and 11 yellow, drawing 6 times with no replacement, what is the chance that at least one is yellow OR the first two draws are the same?

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20 blue balls and 11 yellow, drawing 6 times with no replacement, what is the chance that at least one is yellow OR the first two draws are the same?




I'm not sure my intuition for the solution of the problem is correct, in particular, I have some issue with the addition rule part.



I started out this problem by thinking about the two scenarios:



1) the first two are yellow



2) the first two are blue



I'm a bit confused about the first scenario: P(at least 1 yellow) OR P(first two are the same) if the first two are yellow, that also satisfy the P(at least 1 yellow) so in this case does the probability equal to 1?



Is this similar to flipping a coin P(head) or P(tail)? Or perhaps it's only a "double counted intersection" that we have to subtract out?



I also thought about using compliment to solve this problem but I'm not quite sure if it works this way:



1- [P(no yellow) or P(first two are different)]



thank you!







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  • 2




    Is it a success if both conditions hold? If so, then the answer is $1$ (if there are no yellows drawn then every draw is blue, so, in particular, the first two draws are blue).
    – lulu
    Jul 26 at 21:31






  • 2




    If the first two draws are not the same then there will be at least one yellow
    – Henry
    Jul 26 at 23:08










  • OHHHHHH, I get it now, because we only have 2 types of balls to draw from. No matter what we draw we always satisfy at least 1 of the 2 conditions thus the probability is 1!
    – pino231
    Jul 27 at 2:16














up vote
1
down vote

favorite













20 blue balls and 11 yellow, drawing 6 times with no replacement, what is the chance that at least one is yellow OR the first two draws are the same?




I'm not sure my intuition for the solution of the problem is correct, in particular, I have some issue with the addition rule part.



I started out this problem by thinking about the two scenarios:



1) the first two are yellow



2) the first two are blue



I'm a bit confused about the first scenario: P(at least 1 yellow) OR P(first two are the same) if the first two are yellow, that also satisfy the P(at least 1 yellow) so in this case does the probability equal to 1?



Is this similar to flipping a coin P(head) or P(tail)? Or perhaps it's only a "double counted intersection" that we have to subtract out?



I also thought about using compliment to solve this problem but I'm not quite sure if it works this way:



1- [P(no yellow) or P(first two are different)]



thank you!







share|cite|improve this question

















  • 2




    Is it a success if both conditions hold? If so, then the answer is $1$ (if there are no yellows drawn then every draw is blue, so, in particular, the first two draws are blue).
    – lulu
    Jul 26 at 21:31






  • 2




    If the first two draws are not the same then there will be at least one yellow
    – Henry
    Jul 26 at 23:08










  • OHHHHHH, I get it now, because we only have 2 types of balls to draw from. No matter what we draw we always satisfy at least 1 of the 2 conditions thus the probability is 1!
    – pino231
    Jul 27 at 2:16












up vote
1
down vote

favorite









up vote
1
down vote

favorite












20 blue balls and 11 yellow, drawing 6 times with no replacement, what is the chance that at least one is yellow OR the first two draws are the same?




I'm not sure my intuition for the solution of the problem is correct, in particular, I have some issue with the addition rule part.



I started out this problem by thinking about the two scenarios:



1) the first two are yellow



2) the first two are blue



I'm a bit confused about the first scenario: P(at least 1 yellow) OR P(first two are the same) if the first two are yellow, that also satisfy the P(at least 1 yellow) so in this case does the probability equal to 1?



Is this similar to flipping a coin P(head) or P(tail)? Or perhaps it's only a "double counted intersection" that we have to subtract out?



I also thought about using compliment to solve this problem but I'm not quite sure if it works this way:



1- [P(no yellow) or P(first two are different)]



thank you!







share|cite|improve this question














20 blue balls and 11 yellow, drawing 6 times with no replacement, what is the chance that at least one is yellow OR the first two draws are the same?




I'm not sure my intuition for the solution of the problem is correct, in particular, I have some issue with the addition rule part.



I started out this problem by thinking about the two scenarios:



1) the first two are yellow



2) the first two are blue



I'm a bit confused about the first scenario: P(at least 1 yellow) OR P(first two are the same) if the first two are yellow, that also satisfy the P(at least 1 yellow) so in this case does the probability equal to 1?



Is this similar to flipping a coin P(head) or P(tail)? Or perhaps it's only a "double counted intersection" that we have to subtract out?



I also thought about using compliment to solve this problem but I'm not quite sure if it works this way:



1- [P(no yellow) or P(first two are different)]



thank you!









share|cite|improve this question












share|cite|improve this question




share|cite|improve this question








edited Jul 26 at 23:36
























asked Jul 26 at 21:26









pino231

3268




3268







  • 2




    Is it a success if both conditions hold? If so, then the answer is $1$ (if there are no yellows drawn then every draw is blue, so, in particular, the first two draws are blue).
    – lulu
    Jul 26 at 21:31






  • 2




    If the first two draws are not the same then there will be at least one yellow
    – Henry
    Jul 26 at 23:08










  • OHHHHHH, I get it now, because we only have 2 types of balls to draw from. No matter what we draw we always satisfy at least 1 of the 2 conditions thus the probability is 1!
    – pino231
    Jul 27 at 2:16












  • 2




    Is it a success if both conditions hold? If so, then the answer is $1$ (if there are no yellows drawn then every draw is blue, so, in particular, the first two draws are blue).
    – lulu
    Jul 26 at 21:31






  • 2




    If the first two draws are not the same then there will be at least one yellow
    – Henry
    Jul 26 at 23:08










  • OHHHHHH, I get it now, because we only have 2 types of balls to draw from. No matter what we draw we always satisfy at least 1 of the 2 conditions thus the probability is 1!
    – pino231
    Jul 27 at 2:16







2




2




Is it a success if both conditions hold? If so, then the answer is $1$ (if there are no yellows drawn then every draw is blue, so, in particular, the first two draws are blue).
– lulu
Jul 26 at 21:31




Is it a success if both conditions hold? If so, then the answer is $1$ (if there are no yellows drawn then every draw is blue, so, in particular, the first two draws are blue).
– lulu
Jul 26 at 21:31




2




2




If the first two draws are not the same then there will be at least one yellow
– Henry
Jul 26 at 23:08




If the first two draws are not the same then there will be at least one yellow
– Henry
Jul 26 at 23:08












OHHHHHH, I get it now, because we only have 2 types of balls to draw from. No matter what we draw we always satisfy at least 1 of the 2 conditions thus the probability is 1!
– pino231
Jul 27 at 2:16




OHHHHHH, I get it now, because we only have 2 types of balls to draw from. No matter what we draw we always satisfy at least 1 of the 2 conditions thus the probability is 1!
– pino231
Jul 27 at 2:16










1 Answer
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OR in mathematics is the inclusive or, so if either condition or both is satisfied the sentence is satisfied. OR in English is ambiguous, it can be inclusive or exclusive. Given the problem, I would take it as inclusive here. As you say, that makes the probability $1$. Either the first two balls are blue and hence the same color or at least one of them is yellow. We win either way.






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    1 Answer
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    active

    oldest

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    1 Answer
    1






    active

    oldest

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    active

    oldest

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    active

    oldest

    votes








    up vote
    4
    down vote



    accepted










    OR in mathematics is the inclusive or, so if either condition or both is satisfied the sentence is satisfied. OR in English is ambiguous, it can be inclusive or exclusive. Given the problem, I would take it as inclusive here. As you say, that makes the probability $1$. Either the first two balls are blue and hence the same color or at least one of them is yellow. We win either way.






    share|cite|improve this answer

























      up vote
      4
      down vote



      accepted










      OR in mathematics is the inclusive or, so if either condition or both is satisfied the sentence is satisfied. OR in English is ambiguous, it can be inclusive or exclusive. Given the problem, I would take it as inclusive here. As you say, that makes the probability $1$. Either the first two balls are blue and hence the same color or at least one of them is yellow. We win either way.






      share|cite|improve this answer























        up vote
        4
        down vote



        accepted







        up vote
        4
        down vote



        accepted






        OR in mathematics is the inclusive or, so if either condition or both is satisfied the sentence is satisfied. OR in English is ambiguous, it can be inclusive or exclusive. Given the problem, I would take it as inclusive here. As you say, that makes the probability $1$. Either the first two balls are blue and hence the same color or at least one of them is yellow. We win either way.






        share|cite|improve this answer













        OR in mathematics is the inclusive or, so if either condition or both is satisfied the sentence is satisfied. OR in English is ambiguous, it can be inclusive or exclusive. Given the problem, I would take it as inclusive here. As you say, that makes the probability $1$. Either the first two balls are blue and hence the same color or at least one of them is yellow. We win either way.







        share|cite|improve this answer













        share|cite|improve this answer



        share|cite|improve this answer











        answered Jul 27 at 0:22









        Ross Millikan

        275k21186351




        275k21186351






















             

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