Online Quiz 2

Online Quiz 2 - Maple T.A. - Gradebook

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System Homepage » Class Homepage » Student Details » Student Assignment Details Stat 230 W09 : Gradebook Welcome Po-Wei Chuang [ My Profile ] Assignment detail for Po-Wei Chuang in Online Quiz 2: Po-Wei Chuang Login: pchuang Email: pchuang@uwaterloo.ca Student ID: 20260696 Assignments completed: 22 Assignments active: 0 Question Grade 1 A Veternarian's records show that 30% of all injured dogs are kept in the clinic for treatment, 35% are back to normal health the next day, and 15% are both kept for treatment and back to normal health the next day. If a dog is injured, what is the probability that the dog will be either kept in the clinic, or back to normal health the next day, or both? Answer with a decimal probabilty (e.g. 0.42) or a percentage WITHOUT a % sign (e.g. 42 NOT 42%). Your Answer: 0.61325 Correct Answer: .5 Comment: Define events X = {admitted to clinic}, Y = {back to health next day} . Then you are given P(X) = 0.3, P(Y) = 0.35 and P(XY)= 0.15. The question asks you for P(XUY) = P(X) + P(Y) - P(XY)=.5. In particular you subtract P(XY) to cancel out the "double count" of dogs that meet both criteria. Instructors Comment: 0.0 2 Let A and B be independent events with P(A)= 0.5 and P(B)= 0.3. The probability that either A or B occurs, but NOT both is: Your Answer: 0.65 Correct Answer: 0.5 Comment: Since A and B are independent we have P(AB) = P(A)P(B) = 0.15 Now, P(AUB) = P(A) + P(B) - P(AB) = 0.5 + 0.3 - 0.15 = 0.65 BUT THAT'S NOT THE ANSWER! We still need to subtract off P(AB) again, the first subtraction just took care of "double- counting", now we subtract again to get rid of everything in AB: P(A or B but not both) = 0.65- 0.15 = 0.5 Instructors Comment: 0.0 3 Suppose that A and B are 2 events with P(A) = 0.2, P (A or B) = 0.6. For what value of P(B) would A and B be mutually exclusive?
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This note was uploaded on 03/24/2010 for the course STAT 230 taught by Professor Various during the Winter '06 term at Waterloo.

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Online Quiz 2 - Maple T.A. - Gradebook

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