Question 477872

number of ways to select 5 pens out of 12= 12C5 = 792

probability that no one write  P(A)= 5C5/792 = 1/792

a) probability that at least one write P(A')= 1 - P(A) = 791/792


probability that all write P(B) = 7C5/792 = 21/792

b) 
probability that at least does not write P(B')= 1 - P(B) = 771/792



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