Question

a member of a book club wishes to purchase 2 books from a selection of 8 books recommended for a certain month. in how many ways can she choose them?

\\{}_{n}c_{r} = \frac{n!}{r!(n-r)!}\\

Explanation:

Identify the parameters

$$ n = 8, \quad r = 2 $$

Apply the combination formula

$$ {}_{8}C_{2} = \frac{8!}{2!(8-2)!} = \frac{8!}{2! \cdot 6!} $$

Simplify the expression

$$ {}_{8}C_{2} = \frac{8 \times 7}{2 \times 1} = 28 $$

Answer:

28