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3. A medical investigator is studying two drugs identical in appearance numb ﬂed 1 or 2;
When the drugs are injected in guinea pigs the probabilities that an antitoxin Will develop
are 1/4 for number 1 and 1/3 for number 2, There are two bottles of number 1 and three
bottles of number 2. The investigator, in hurrying to give a demonstration of these drugs,
takes one bottle without noting its number. In transit the label is torn off (a) \Vhat is the probability that the selected bottle is number 1? ::
\§ 1,: , .» /§* (b) What is the probability that the selected bottle is number 2‘? . r v_._ 4 WV
‘ ’7/5 ,
\
\v ‘x, (c) What is the probability that no antitoxin forms for number 1'?
“V“: {3 ”‘1‘ \ ,« i ‘ w it; {l \llx‘} (d) What is the probability that no antitoxin forms for number 2? '2.
" \ m, :15" 2 ,y g i Z 1
10‘1" g’Ql 1 t ' , {i 2) l 3 ,1? (c) When a guinea pig is injected with this drug, no antitoxin forms. What is the probability
that it was drug number 27 hint: P(A)P(F§ A) P A B‘  x
< l ) P(A)P(B[A) + P(ACJP(BAC)
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 Spring '08
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