Question 508317
What is the probability that the student is a sophomore given he doesn't carry a credit card?

Class 	Credit Card Carrier 	Not a Credit Card Carrier 	Total
Freshman 	33 	27 	60
Sophomore 	6 	24 	40
Total 	        39 	61 	100

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P(soph | carries card) 
= P(soph AND cc)/P(cc) 
= (24/100)/(61/100)
= 24/61
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P(choice | condition)
Note: The easy way to find these answers
when you have a contingency chart is to
remember that the "conditional" is the 
universe and the choice is a subset of
of the conditional.  So your conditional
has 61 and your choice has 24.  So your
answer is 24/61.
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Cheers,
Stan H.
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