Examples for 10610
1. Jake is deciding what to do with his Friday night. In the past he went to the bar with friends
with a probability of .2, and the rest of the time he went to the girlfriend’s house.
If he was at the
bar, he went home with 70% of the time, and he went to jail the rest of the time. If he was at the
girlfriend’s house, he went home only 10% of the time, and he stayed the rest of the time. If he
went to the bar and then home, he was happy 95% of the time. If he went to the bar and jail, he
was happy only 1% of the time. 18% of all Friday nights, Jake went to the girlfriend’s house,
stayed, and was happy about it. 4.8% of all Friday nights, Jake went to his girlfriend’s house,
went home afterward, and was happy about it. Use the past information provided to find the
following probabilities:
P(Jail)
P(Jail) = P(Bar) * P(Jail  Bar) = .2*.3 = .06 (This uses
the general multiplication rule).
P(Home)
P(H) = P(B)*P(H  B) + P(GF)*P(H  GF) = .2*.7 + .8*.1 = .22 (This uses the law of total
probability).
P(Girlfriend’s  Home)
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 Fall '08
 MARTIN
 Probability

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