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i have come up against a question i do not understand
Box a has 5 balls one blue and 4 yellow
box b has five balls three blue and 2 yellow
find the probability the ball is yellow I am having problem because there are two bags and i am not sure how to put this in equation form

this is as far as I have gotten(4/9)*(2/5)=8/45 or 17.77%

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  • $\begingroup$ What does your question title have to do with the question? What does it tell anybody about your question? Do you know the difference between upper case and lower case? Does your computer not have a caps lock button? The understanding that you seek will come from within - trying to get others to do your work for you is not the right path. $\endgroup$
    – wolfies
    Jun 16, 2014 at 17:08
  • $\begingroup$ Sorry I am new to this whole thing I have a question about how to figure this and i haven't taken a math course in 20 years so I am lost at every turn $\endgroup$
    – john
    Jun 16, 2014 at 17:11

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assuming what you meant was 'what's the probability of sampling a yellow ball', you should use the law of total probability: $$ P(Y) = P(Y|B_1)P(B_1) + P(Y|B_2)P(B_2) $$ the probabilities to sample from either box are equal, as I understand.

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I assume you mean "the probability of drawing a yellow ball from each box" or something similar?

In that case, it's the probability of A multiplied by the probability of B. The two events are entirely disjoint, you see. That is, box A does not care about what you do later with box B, and box B cares not for what happened in box A.

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  • $\begingroup$ one ball chosen at random from one box you chose at random? $\endgroup$
    – john
    Jun 16, 2014 at 17:12
  • $\begingroup$ Are you asking me? :) but in that case, the total probability is the sum of the probabilities of picking A and drawing yellow, and picking B and drawing yellow. $\endgroup$
    – Christofer Ohlsson
    Jun 16, 2014 at 17:15

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