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In 8 .1, we have a bag containing three blue marbles and two red.
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We take a marble, put the marble aside.
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Take a second marble.
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We want to start by drawing a three diagram here.
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So we'll have the first choice.
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It might be blue, it might be red.
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Then we have the second choice.
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Again, it might be blue, might be red.
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Now, what's the probability? the first marble is blue.
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Well, we have five marbles in the bag, three of them are blue, so that's a three out of five chance.
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And a 2 out of 5 chance it is red.
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Now let's pretend the first one is blue.
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We take out of blue marble, put it to one side, go back in for a second.
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What's the probability the second is blue? well, there are only 4 left and only 2 of them are blue.
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So 0 .5 and 0 .5 for red.
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If the first marble is red, well, there are 4 marbles left, 3 blue, 1 red.
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So a 0 .75 and 0 .25 chance, respectively.
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Three out of four and one out of four.
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So there's the branches and at the end to combine the probabilities you multiply.
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So 0 .6 times 0 .5 is the probability of blue, blue, 0 .3 for blue red, 0 .4 times 0 .75 is 0 .3 for red blue, and 0 .3, no, no, i wish, 0 .1 for red, red.
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So those are the possible outcomes.
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Notice they do add up to 1 or 100%, because we know one of these is going to happen.
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What's for probability of getting a red followed by a blue in that order? well, that is red blue, that is 0 .3.
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8 .2.
01:53
We have two events...