<PRE><B>Question 1127625</B>
On a bookshelf, there are five different mystery books and six different biographies. How many different sets of four books can Emilio choose if two books must be mystery books and two of the books must be biographies? 
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Two mystery books:: 5C2 = (5*4)/(1*2) = 10 sets
Two biography books:: 6C2 = (6*5)/(1*2) = 15 sets
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Ans:: # of combined sets:: 10*15 = 150 sets
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Cheers,
Stan H.
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