Final answer:
To determine how many ways an instructor can select 3 textbooks from 18, we use the combination formula which results in 816 ways.
Step-by-step explanation:
Calculating Combinations
The question asks how many ways an instructor can select 3 textbooks from a possible 18 textbooks. This is a problem of combinations where order does not matter, and it can be solved using the combination formula C(n, k) = n! / (k!(n - k)!), where n is the total number of items to choose from, k is the number of items to choose, and ! denotes factorial. The formula for our problem is C(18, 3) = 18! / (3!(18 - 3)!). After simplifying, we obtained 816 as the number of ways to select 3 textbooks from 18.
If a student is interested in expanding their knowledge of combinations, they can do so by practicing to systematically list out all the possibilities and understanding the principles of factorial multiplication as illustrated in the combined use of multiplication to represent choices at each stage.