Question 1201252
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Assuming the books are different / distinguishable, there are


    {{{C[15]^3}}}.{{{C[12]^3}}}.{{{C[9]^3}}}.{{{C[6]^3}}}.{{{C[3]^3}}} = 

        = 455*220*84*20*1 = 168168000 different ways.    <U>ANSWER</U>
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Solved and explained.