we have given that list of 15 books from that we need to choose 4 books.
we need to find how many different choices are made.
we know that formula is [tex] nCr_ [/tex].
where n is the number of books and r is number of books chosen.
[tex] 15C_{4}_ =(15*14*13*12)/(1*2*3*4)=1365 [/tex] choices can be made.
