Question 392131
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Hi
12 books, 7 of which are novels and 5 of which are biographies
Total ways of choosing 4 books from a group of 12 books =  12C4
P(2 novel 'and' 2 biographies) = 7C2*5C2/12C4 =  21*10 /495 = .4242
where nCx = {{{n!/(x!(n-x!))}}}