A student creates a function to represent the cost of pencils available for purchase at the school store. The school charges 5 cents per pencil for up to 20 pencils. What is the domain of the function?

ANSWER
All integers from 0 to 20
EXPLANATION
The cost per pencil is 5 cents for any number of pencils up to 20, which indicates that the domain is a number of pencils less than or equal to 20. Because the number of pencils must be a positive integer, the domain of this function is all integers from 0 to 20.