Question

Haley pays a monthly fee of $20 for her cell phone and then pays 5 cents per minute used. The total cost of Haley’s monthly cell phone bill can be expressed by the function C(m) = 0.05m + 20, where m is the number of minutes used. What are the domain and range of the function C(m)?

Answer 1

Domain: m ≥ 0 (interval notation: [0, ∞)).
Range: C(m) ≥ 20 (interval notation: [20, ∞)).

(If you restrict m to whole minutes, domain is {0,1,2,...} and range is {20 + 0.05k | k ∈ Z, k ≥ 0}.)