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anonymous

  • 5 years ago

The probability of randomly selecting a red marble from a bag, replacing it, and selecting a red marble again is 1/25. What is the probability of selecting a red marble on the first try?

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  1. anonymous
    • 5 years ago
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    \[\frac{1}{25}\]

  2. anonymous
    • 5 years ago
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    I will become your fan and give you a medal for the right answer

  3. anonymous
    • 5 years ago
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    reason: same number of marbles in the bag the second time as the first. same number of red marbles the second time as well. so nothing has changed and the probabilities are the same.

  4. anonymous
    • 5 years ago
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    oh thanks!

  5. anonymous
    • 5 years ago
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    oh wait. i need to read the question more carefully. hold on.

  6. anonymous
    • 5 years ago
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    hold on i think i was mistaken. sorry.

  7. anonymous
    • 5 years ago
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    i misread. let me try again and this time go slow, and maybe with an explanation.

  8. anonymous
    • 5 years ago
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    ok

  9. anonymous
    • 5 years ago
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    put A = the event you select a red marble on the first try. we want \[P(A)\] B = event you select a red marble on second try.

  10. anonymous
    • 5 years ago
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    \[A\cap B\] is the even that both marbles selected were red, and you are given that \[P(A\cap B)=\frac{1}{25}\] because you are given that the probability that both marbles selected were red

  11. anonymous
    • 5 years ago
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    in general \[P(A\cap B) = P(A)\times P(B|A)\] but since you have replaced the red marble there are the same number of red marble in the bag and the same number of marbles, so \[P(B)=P(A)\]

  12. anonymous
    • 5 years ago
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    Shouldn't it be 1/5. 1/5 * 1/5 = 1/25 th

  13. anonymous
    • 5 years ago
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    therefore you have \[\frac{1}{25}=P(A)\times P(A)\] so \[P(A)=\frac{1}{5}\]

  14. anonymous
    • 5 years ago
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    That is the probability of selecting it once into the same probability of it being picked again

  15. anonymous
    • 5 years ago
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    yes you are right isan_meswani. my first answer was a mistake. i read the problem incorrectly.

  16. anonymous
    • 5 years ago
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    1/5? not1/25?

  17. anonymous
    • 5 years ago
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    yes, 1/5

  18. anonymous
    • 5 years ago
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    sorry i messed you up on first try.

  19. anonymous
    • 5 years ago
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    Suppose you know there are originally 2 red marbles in the bag. How many marbles are there in all?

  20. anonymous
    • 5 years ago
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    Now this is simple, isn't it? its 10

  21. anonymous
    • 5 years ago
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    really?

  22. anonymous
    • 5 years ago
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    yes that was an easy one. \[\frac{1}{5}=\frac{2}{x}\]

  23. anonymous
    • 5 years ago
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    oh thanks!

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