How do I solve these two problems?

noname1234

New member
Joined
Apr 1, 2006
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12
1. The probablity that a person with certain symptoms has hepatitis is 0.82. A blood test gives positive results for 89% of those who have the disease and 6% of those without th disease. What is the probablity that a person with the symptoms who reacts positively to the test has hepatitis?

2. In a state lottery, the player buys a ticket for $2.00 and chooses any 3-digit number from 000 to 999. The wininng number receives $500. Find the expected winnings.

thank you!!!!
 
1.
Symptoms with disease .82
positive test reaction .89
both .82*.89 = .7298

Symptoms without disease .18
positive test reaction .06
both .18*.06 = .0108

Total positives = .7298+.0108 = .7406
Has disease .7298/.7406 = 98.5%

2.
$500*(1/1000) = 50¢
Investement $2
Winnings -$1.50
 
Well, I got the same answer as you for the first one, but for the 2nd one I got 50 cents. Did anyone else get that? :shock:
 
Look at my post again. It depends on your definition of winnings. You paid $2 for the ticket. Yes, you win an average of 50¢ but you end up with -$1.50 on average. I suspect that is the answer they want or they wouldn't have mentioned the cost of the ticket.
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Gene
 
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