Question

There are 11 books on your bookshelf. This summer you plan to read 5 books. How many different combinations of 5 books could you select from your bookshelf of 11 books? 462 11 55,440

Answer 1

= 462

Explanation:

the number of combinations is = n! / r!(n - r)!

where n = total number and r is the number you select. For this equation, the order of the items chosen does not matter. (So if I pick book A, then B, then C, then D, then E, that's the same thing as B, A, C, E, D. Order doesn't matter; it's the same exact set of 5 books.)

So in this example:

n = 11

r = 5

= n! / r!(n - r)!

= 11! / 5! (11-5)!

= 11! / 5! (6)!

= 462