## Problem B6 Practice Final |
Soniakumr |
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Would the answer be [(10choose2)(5choose1) + (5choose3)]/[(10choose2)(5choose1) + (5choose2)(10choose1) + (5choose3)] |

Lilyhui: March 19, 2015, 8:25 p.m. |
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The decimal answer is 0.5604 |

Lilyhui: March 19, 2015, 8:27 p.m. |
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You also "pretend" that you have the third green already and do the calculations that way. The answer would then be (10 C2)+(4C2) divided by (14C2) |

katsue13: March 19, 2015, 8:59 p.m. |
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I did this problem using the tree method and got a different decimal answer. Is this wrong? |

Lilyhui: March 19, 2015, 9:05 p.m. |
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I did the tree method and got (10*9*5+5*4*3)/(10*9*5+5*4*3+10*5*4+5*10*4). I cancelled out the 15*14*13 since they appear in both denominators |

katsue13: March 19, 2015, 9:06 p.m. |
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Using the tree, my answer was (3/13)*(5/15)*(4/14) + (10/15)*(9/14)*(5/13) |

Lilyhui: March 19, 2015, 9:19 p.m. |
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I wish there was a way to upload a picture because the tree gets pretty big (you should end up with 8 branches). Maybe start with conditional probability again (you should divide with your answer with prob that the third ball is green) |