Allergic reactions to poison ivy can be miserable.
Allergic reactions to poison ivy can be miserable. Plant oils cause
the reaction. Researchers at Allergy Institute did a study to determine the effects of washing the oil off within 5 minutes of exposure. A random sample of 1000 people with known allergies to poison ivy participated in the study. Oil from the poison ivy plant was rubbed on a patch of skin. For 500 of the subjects, it was washed off within 5 minutes. For the other 500 subjects, the oil was washed off after 5 minutes. The results are summarized in the following table.
Reaction Within 5 Minutes After 5 Minutes Row Total
None. 402. 63. 465
Mild. 67. 321. 388
Strong. 31. 116. 147
Column Total. 500. 500 1000
Let’s use the following notation for the various events: W = washing oil off within 5 minutes, A = washing oil off after 5 minutes, N = no reaction, M = mild reaction, S = strong reaction. Find the following probabilities for a person selected at random from this sample of 1000 subjects. (Use 3 decimal places.)
(a) P(N) = .465
P(M) .388
P(S) .147
(b) P(N | W)=
P(S | W)=
(c) P(N | A)=
P(S | A) =
(d) P(N and W) =
P(M and W) =
(e) P(N or M). =