Answer
$495$
Work Step by Step
A combination from a group of items occurs when no item is used more than once and the order of items makes no difference.
The number of combinations possible if $r$ items are taken from $n$ items is
${}_{n}C_{r}=\displaystyle \frac{n!}{(n-r)!r!}$
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It does not matter which book was chosen first, second,...
Order is not important, we deal with combinations.
${}_{12}C_{4}=\displaystyle \frac{13!}{(12-4)!4!}=\frac{12\times 11\times 10\times 9}{1\times 2\times 3\times 4}$
=$11\times 5\times 9=495$
