Question 566641
What is the probability that the student is a freshman 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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Ans: P(F | C') 
= P(F AND C')/ P(C') 
= (27/100)/(61/100) 
= 27/61
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Notice that, when you have a conditional like this (C'), that 
conditional becomes your Universe.
Cheers,
Stan H.